Posts Tagged ‘agronomic crop insect scouting’

Agronomic Crop Insects

Friday, September 21st, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Small Grains
As you make plans to plant wheat, be sure to review our article on aphid and barley yellow dwarf management in the Aug 3, 2012 newsletter (http://agdev.anr.udel.edu/weeklycropupdate/?p=4595). The following link to the May 1, 2012 Kentucky’s Pest News also provides additional management information, especially as it relates to the weather conditions in the 2012 season (http://www.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/kpn_12/pn_120501.html).

Agronomic Crop Insects – September 14, 2012

Friday, September 14th, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Alfalfa
Continue to sample fields on a weekly basis for defoliators including earworm, webworms and all armyworm species. We continue to get reports of fields with economic levels of defoliators. Although we have limited experience at this time of year with damage to re-growth, it will be important to check for the presence of larvae to determine if they are still present and holding back the re-growth.

Soybeans
Where economic populations levels of corn earworm are still present, late planted soybean fields that still have susceptible pods will still be at risk from pod damage. If economic levels of defoliators (i.e. worm defoliators including soybean looper, beet armyworm and green cloverworm) are present, you will also need to consider the maturity of the crop as well as the health of the leaf canopy to make a treatment decision. In an article related to defoliation from soybean loopers, entomologists and agronomists in the south suggested that if economic levels are present:

“Fields will need to be protected as long as the pods are still green and until the lower leaves are just beginning to yellow. This should correspond, more or less, with the R6.5 stage (10 days after R6.0 = full green seed). If leaves are beginning to yellow up the stem, not from drought but from the maturity process, and there are any pods on the plant that are beginning to yellow, the field should be safe, that is no need to treat. Next you have to determine the health of the leaf canopy: is it robust, average, or thin. Each can tolerate different amounts of leaf loss before reducing yield potential. Robust fields (mid chest or higher) can tolerate a lot of feeding. Average fields (upper thigh to mid chest) can tolerate normal amounts of feeding. Thin canopy fields (mid thigh or below) cannot tolerate additional leaf loss. Also in this canopy assessment, you need to take a stab at estimating the current percent defoliation. This is not an exact measure, but your best estimate looking over the entire canopy top to bottom. The eyes tend to focus on those badly defoliated top leaves. Look beyond those and try to come up with an overall average.”

When it comes to stinkbugs, you should continue scouting until the latest planted fields reach the R7 growth stage (a few studies in the south even say through the R-7 stage) when beans should no longer be susceptible to stink bug feeding.

You will still need to consider the potential for grasshoppers and bean leaf beetles to feed on pods. Although bean leaf beetle populations have been generally low this past season, there are still some hot spots of activity, so you will need to examine pods for feeding damage. During the last wet fall, we did see significant pod scarring late in the season that resulted in moldy beans. Information from Ohio indicates that a “treatment is usually indicated when pod feeding reaches 10-15% and beetles are still present and actively feeding. In fields where the pods have started turning yellow and brown, the adults will be leaving in search of greener pastures”.

If you do need to treat, be sure to check the label for the pre-harvest interval (time needed between last application and harvest) as well as other restrictions, including rotational restrictions.

Agronomic Crop Insects – September 7, 2012

Friday, September 7th, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Soybeans
We continue to find corn earworms in soybeans. If you have not checked your fields, be sure to sample fields so you do not miss a late hatch of larvae. Although trap catches appeared to be declining on September 3, we will need to watch trap catches at the end of this week to see if this trend continues. In addition, we need to watch what happens in states to our south.

A number of defoliators are still present in double crop beans. The threshold for defoliation will need to be reduced if a mixed population is present. Although soybean looper populations remain low, there are reports from the southern states of building populations.

In New Castle and Kent Counties, we are a finding a few more fields with high levels of Brown Marmorated Stink Bugs on field edges of full season soybeans. Although we do not have a threshold for BMSB, we are also finding levels that we use as a threshold for native stinkbugs (2.5 per 15 sweeps) along the edges of double crop fields in New Castle County. Native stink bugs populations continue to be at threshold levels in fields throughout the state.

Small Grains
As you make plans to plant small grains, you need to remember that Hessian fly can still be a problem. Since the fly survives as puparia (“flax seeds”) in wheat stubble through the summer, you should still consider this pest as you make plans to plant small grains. In our area, damage has generally been the result of spring infestations. Plants attacked in the spring have shortened and weakened stems that may eventually break just above the first or second node, causing plants to lodge near harvest. Warm fall weather conditions can extend fly emergence and egg-laying beyond the fly-free dates, but these dates should still be used as a guideline for planting. Plants attacked in the fall at the one-leaf stage may be killed outright. Wheat attacked later in the fall will be severely stunted, with the first tillers killed and plant growth delayed. Plants infested in the fall can easily be recognized by their darker than normal bluish coloration and leaves with unusually broad blades. Combinations of strategies are needed to reduce problems from Hessian fly:

● Be sure to completely plow under infested wheat stubble to prevent flies from emerging.

● Avoid planting wheat into last season’s wheat stubble, especially if it was infested with Hessian fly.

● Avoid planting wheat next to last season’s wheat fields – the most serious infestations can occur when wheat is early planted into wheat stubble or into fields next to wheat stubble.

● Eliminate volunteer wheat before planting to prevent early egg-laying.

● Do not use wheat as a fall cover crop near fields with infestations.

● Plant after the fly-free date. (Oct 3 – New Castle County; Oct 8 – Kent County; Oct 10 – Sussex County).

● Plant resistant varieties. You should look for varieties that have resistance to Biotype L. You will need to check with your seed dealers to identify varieties that our adapted our area.

The following link from Alabama provides additional information on Hessian Fly Management (http://www.aces.edu/dept/grain/HessianFly.php

Agronomic Crop Insects – August 31, 2012

Friday, August 31st, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Alfalfa
Continue to sample fields on a weekly basis for defoliators including earworm, webworms and all armyworm species. Economic levels of defoliators, continue to be found causing damage.

Soybeans
We can still find fields with economic levels of corn earworm (mainly double crop), stink bugs and defoliators. There have also been a few fields that need a second corn earworm spray for recently hatched larvae.

As soybeans begin to mature and insects are still active in fields, there is always the question regarding the susceptibility of fields to insect damage, especially full season soybeans. So let’s discuss each group and what we know and/or what experience we have from past seasons.

Stink Bugs
As a general rule, soybeans are still susceptible to damage from stink bugs through growth stage R6.5 (“mid R6”). This has been described by some agronomists as the stage when pods are still green and the lower leaves are just beginning to yellow from natural senescence and not drought stress – approximately 10 days after R6.0 (full green seed). It has also been described by others as mid-way from full seed development until maturity. However, there are a few studies from the south indicating that scouting is needed until beans are in the R-7 growth stage (beginning seed maturity) to avoid damage from stinkbugs which can include underdeveloped or aborted seeds, green stem syndrome, reductions in pod fill, seed vigor and viability, yield loss and a reduction in the storage stability of harvested seeds. In New Castle and Kent Counties, we are starting to see fields with high levels of Brown Marmorated Stink Bugs on field edges of full season soybeans (most fields are growth stage R6). If a treatment is needed, an edge treatment (one spray boom width – at least 50 ft wide) was effective last year, and we are working on a regional project to document the outcome of this strategy in 2012. There are also areas of the state with high native brown and green stink bug populations so be sure to scout for them as well.

Corn Earworms
As far as corn earworms, the experience of most entomologists in the region is that soybeans are most susceptible to corn earworm damage when beans are in the R-5 and early R6 stages although there are cases where we see damage through the R6.5 stage. As of Aug 27, a number of our corn earworm pheromone traps where still catching high numbers of moths so it is too early to say for sure if populations are on the decline (http://ag.udel.edu/extension/IPM/traps/latestblt.html). In addition, trap catches in North Carolina are still high and weather patterns could bring these moths north. We sometimes see a late summer/early fall corn earworm flight which could result in new worm infestations. Most full season fields should be in the “bug-safe” late R6-R7 stage if this occurs; however, double crop soybeans will still be susceptible to attack.

Defoliators
When it comes to defoliators, especially soybean loopers, it is important to keep scouting for them as well through the R6.5 stage. We continue to find pockets of soybean loopers and beet armyworms. If leaves are beginning to yellow up the stem, not from drought but from the maturity process, and there are any pods on the plant that are beginning to yellow, the field should be safe from most defoliators. The exceptions would be grasshoppers and bean leaf beetles, which can scar pods later in the growth stage of soybeans.

NOTE: As we get closer to harvest, be sure to check all labels for the days from last application to harvest as well as other restrictions.

Small Grains
With the increase in no-till wheat acreage as well as our typical rotation of wheat following corn, it will be important to consider a number of insect pests that can present problems. The following article provides a good review of insect pests that pose a threat to wheat in the fall including aphids, the wheat curl mite, Hessian fly and fall armyworm. (http://www.uky.edu/Ag/kpn/kpn_08/pn080825.htm#wheins). In addition to the insect pests listed in this article, true armyworms have been a pest in the past as well as slugs if we have a wet fall.

Agronomic Crop Insects – August 24, 2012

Friday, August 24th, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Soybeans
Be sure to continue to scout carefully for earworms as well as defoliators during the next few weeks. As we get closer to harvest be sure to check all labels for the days between last application and harvest.

Threshold levels of corn earworm continue to be found in fields in Kent and Sussex counties but they are not present in every field. Although we can find various sizes of larvae, in most cases they are still relatively small. In addition they are being found in some full season (especially where canopy is not closed) and double crop fields so the only way to know if you have an economic level will be to scout. If fields were already sprayed, be sure to watch for newly hatched larvae. With the sustained flights, we are starting to see a new hatch of small larvae.

Since last week’s report, we also are starting to find an increase in stinkbugs, especially in full season fields. The population levels as well as species vary from field to field depending on your location in the state. In Sussex County, the predominant species are native green and brown stink bugs. From the Milford and Harrington areas in Kent County through New Castle County, the brown marmorated stink bug (BMSB) can be found in the mix. We are just starting to find a few hot spots of BMSB with the highest populations generally still along woods edges. You will need to continue to scout for stinkbugs in fields that are in the pod development and pod fill stages. Economic damage is most likely to occur during these stages. You will need to sample for both adults and large nymphs when making a treatment decision. Available thresholds are based on beans that are in the pod development and fill stages. We are currently following the same guidelines that are being used in Virginia. Thresholds are based on numbers of large nymphs and adults (native green and/or brown stink bugs), as those are the stages most capable of damaging pods. As a general guideline, current thresholds are set at 2.5 per 15 sweeps in narrow-row beans, or 3.5 per 15 sweeps in wide-row beans.

Once again we are finding a few fields with high levels of whiteflies. Although we have limited experience with whiteflies in our area, as far as we know, whiteflies have generally not been a problem in the past, especially if moisture is adequate. They are related to aphids (that is they are in the same order of insects) and so can cause yellowing on the leaves if populations are high enough. Damage is most likely to occur when beans are stressed. The following links provides pictures of whiteflies and some additional comments regarding whiteflies in soybeans: http://bulletin.ipm.illinois.edu/article.php?id=832

http://ipcm.wisc.edu/blog/2012/07/questions-about-whiteflies-in-soybean/

We continue to find a significant number of defoliators including beet armyworm (BAW), fall armyworm, yellow striped armyworm, green cloverworm, soybean loopers and grasshopper in double crop and a few full season fields. All of these insects are defoliators and you will need to use percent defoliation to make a treatment decision. There are no available thresholds for the number of the above insects per sweep. Remember, that in addition to defoliation, grasshoppers can feed on and/or scar pods. In full season soybeans in the pod fill stage, the threshold is 10-15% defoliation. Remember, double crop soybeans cannot tolerate as much defoliation since they often do not reach the leaf area index needed for maximum yields. As a reminder, the pyrethroids have not provided effective control of beet armyworm or soybean loopers so a product labeled for these 2 species in soybeans will be needed if defoliation is present.

Since many of our pests in soybeans migrate to us from the south, the following two links provide information on what is occurring in Virginia and North Carolina:
http://www.sripmc.org/Virginia/
http://www.nccrops.com/.

Agronomic Crop Insects – August 17, 2012

Friday, August 17th, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Alfalfa and Grass Hay Crops
Continue to watch for defoliators in grass hay crops and alfalfa. It is important to catch populations before significant damage has occurred and when larvae are small. In addition to checking labels for rates, be sure to check for all restrictions including but not limited to comments on control under high populations and size of larvae; days to harvest and forage/silage restrictions. Be sure to also scout alfalfa for leafhoppers. Once yellowing has occurred, significant in season damage and long term stand damage has already occurred

Soybeans
Economic levels and hot spots of high levels of corn earworm larvae continue to be found full season and double crop fields in Kent and Sussex counties but they are not present in every field. In general, most larvae are small to medium in size, and occasional large larvae can be found. Since population levels vary from field to field, the only way to know if you have an economic level will be to scout all fields. Remember, corn earworms can feed on the foliage and blossoms as well as the pods. Although there is no threshold for corn earworm feeding on flowers or leaves, data from North Carolina has indicated that feeding on flowers can result in reduced yields by delaying pod set. When looking at foliage feeding by corn earworm, you will need to use defoliation as well as the presence of worms to make a decision (again – there is no worm threshold available for leaf and/or blossom feeding). Once pods are present, the best approach to making a decision on what threshold to use for corn earworm is to access the Corn Earworm Calculator developed at Virginia Tech (http://www.ipm.vt.edu/cew/) which estimates a threshold based on the actual treatment cost and bushel value you enter. Remember, this threshold calculator was developed only for corn earworm.

Be sure to scout for stinkbugs in fields that are in the pod development and pod fill stages. Economic damage is most likely to occur during these stages and a combination of species can be found in fields throughout the state. You will need to sample for both adults and nymphs when making a treatment decision. Available thresholds are based on beans that are in the pod development and fill stages. As a general guideline, current thresholds for native stink bugs are set at 1 large nymph/adult (either brown or green stink bug) per row foot if using a beat sheet, or, 2.5 per 15 sweeps in narrow-row beans, or 3.5 per 15 sweeps in wide-row beans. We do not have a threshold for brown marmorated stink bugs (BMSB).

We continue to find a significant number of defoliators including beet armyworm (BAW), fall armyworm, yellow striped armyworm, green cloverworm and grasshopper in double crop and a few full season fields. All of these insects are defoliators and you will need to use percent defoliation to make a treatment decision. There are no available thresholds for the number of the above insects per sweep. Remember, that in addition to defoliation, grasshoppers can feed on and/ or scar pods. In full season soybeans in the pod fill stage, the threshold is 10-15% defoliation. Remember, double crop soybeans cannot tolerate as much defoliation since they often do not reach the leaf area index needed for maximum yields. As a reminder, the pyrethroids will not provide effective control of beet armyworm so a product labeled for beet armyworm in soybeans will be needed if defoliation is present.

Soybean looper populations are also starting to increase. Identification can be difficult because although there is a “black footed” phase of the soybean looper there is also a “green phase” that can be confused with cabbage loopers. One characteristic that might help is the presence of microspines on soybean loopers that are not present on cabbage loopers; however, you will need high magnification to see the microspines. Soybean loopers are a migratory pest, difficult to control and pyrethroid resistance has been documented in states to our south.

Agronomic Crop Insects – August 10, 2012

Friday, August 10th, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Alfalfa and Grass Hay Crops
As indicated in last week’s newsletter, you need to continue to watch for defoliators in grass hay crops and alfalfa. Significant damage has occurred in a number of grass hay fields from true armyworm and fall armyworm. It is important to catch populations before significant damage has occurred and when larvae are small. In addition to checking labels for rates, be sure to check for all restrictions including but limited to comments on control under high populations and size of larvae; days to harvest and forage/silage restrictions.

Soybeans
Economic levels of corn earworms in Kent and Sussex counties in Delaware and on the lower eastern shore of Maryland. Trap catches continue to increase throughout the state and moths can be found laying eggs in fields. It appears that we could see an extended moth flight and egg laying period in soybeans. Since population levels vary from field to field, the only way to know if you have an economic level will be to scout all fields. Remember, corn earworms can feed on the foliage and blossoms as well as the pods. Although there is no threshold for corn earworm feeding on flowers or leaves, data from North Carolina has indicated that feeding on flowers can result in reduced yields by delaying pod set. When looking at foliage feeding by corn earworm, you will need to use the defoliation threshold as well as the presence of worms to make a decision (again – there is no worm threshold available for leaf and/or blossom feeding). Once pods are present, the best approach to making a decision on what threshold to use for corn earworm is to access the Corn Earworm Calculator developed at Virginia Tech (http://www.ipm.vt.edu/cew/) which estimates a threshold based on the actual treatment cost and bushel value you enter.

Be sure to scout for stinkbugs in fields that are in the pod development and pod fill stages. Economic damage is most likely to occur during these stages and a combination of species can be found in fields throughout the state. You will need to sample for both adults and nymphs when making a treatment decision. Available thresholds are based on beans that are in the pod development and fill stages. As a general guideline, current thresholds for native stink bugs are set at 1 large nymph/adult (either brown or green stink bug) per row foot if using a beat sheet, or, 2.5 per 15 sweeps in narrow-row beans, or 3.5 per 15 sweeps in wide-row beans. We do not have a threshold for brown marmorated stink bugs (BMSB).

We continue to find beet armyworm (BAW) in fields in Kent and Sussex counties. Since this insect is primarily a defoliator, you should use the defoliation thresholds to make a treatment decision. As a reminder, the pyrethroids will not provide effective control so a beet armyworm product labeled for soybeans will be needed if the defoliation threshold is reached.

We continue to sample fields statewide for both Brown Marmorated Stink Bugs (BMSB) and Kudzu Bug, projects funded by the Delaware Soybean Board. We are finding very low levels of BMSB and so far no Kudzu Bugs have been detected. In speaking with my colleague Ames Herbert from Virginia Tech, he indicated that they have found Kudzu Bug in 17 counties but they are still only finding adults. These adults are very mobile so we will need to remain vigilant. Thresholds developed in the south are based on nymphal counts. Please view the following link for pictures of adults and nymphs.

http://www.nccrops.com/2011/06/24/kudzu-bug-confirmed-in-34-north-carolina-counties/

Agronomic Crop Insects – August 3, 2012

Thursday, August 2nd, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Alfalfa and Grass Hay Crops
We are starting to hear reports of the first occurrence of defoliators in hay crops. Fall armyworm can cause significant damage in grass hay so be sure to watch carefully since early detection is important to achieve effective control with labeled products. In alfalfa, a number of defoliators can cause problems including corn earworm, fall armyworm, beet armyworm and webworms. No thresholds are available; however, controls should be applied before significant defoliation occurs.

Soybeans
We continue to find fields with economic levels of spider mites. In areas that have received rain, it generally has helped beans to grow; however, if economic populations were present before the rain they can still be found. As a reminder, under heavy mite pressure and extended hot, dry weather, it often takes an extended period of free moisture on leaves, high humidity during the day and cool evening temperatures to get an increase in the fungal pathogens that can significantly reduce exploded mite populations. In many years, populations can start to decline by mid-August and we have started to find a few diseased mites. However, we are not seeing a significant decline in populations so it is important to continue to scout and apply controls if economic populations are present.

Be sure to scout for stinkbugs in fields that are in the pod development and pod fill stages. Economic damage is most likely to occur during these stages and a combination of species can be found in fields throughout the state. You will need to sample for both adults and nymphs when making a treatment decision. Available thresholds are based on beans that are in the pod development and fill stages. As a general guideline, current thresholds for native stink bugs are set at 1 large nymph/adult (either brown or green stink bug) per row foot if using a beat sheet, or, 2.5 per 15 sweeps in narrow-row beans, or 3.5 per 15 sweeps in wide-row beans. We do not have a threshold for brown marmorated stink bugs (BMSB).

Corn earworm moth trap catches continue to increase and larvae can be found in fields in Kent and Sussex counties. Be sure to scout both full season and double crop soybeans for this insect pest. Only time will tell if we will have a corn earworm outbreak in soybeans in our area. As we have seen in past years, trap catches can give an indication of the potential for a problem; however, only scouting on a routine basis will tell you if you have an economic problem. In the past, we have used the treatment threshold of 3 corn earworms per 25 sweeps in narrow fields and 5 corn earworms per 25 sweeps in wide row fields (20 inches or greater). These are static thresholds that were calculated for a 10-year average soybean bushel value of $6.28. A better approach to determining a threshold is to access the Corn Earworm Calculator (http://www.ipm.vt.edu/cew/) which estimates a threshold based on the actual treatment cost and bushel value you enter.

Consultants have also found a significant increase in beet armyworm (BAW) populations and defoliation. Since this insect is primarily a defoliator, you should use the defoliation thresholds to make a treatment decision. As a reminder, the pyrethroids will not provide effective control so a beet armyworm product labeled for soybeans will need to be applied.

Agronomic Crop Insects – July 27, 2012

Friday, July 27th, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Alfalfa
Continue to scout fields on a weekly basis for leafhoppers and defoliators including corn earworm, webworms, fall armyworm and beet armyworm. Larvae must be small to achieve effective control. Defoliators can be destructive, especially during drought conditions. When defoliators are present, early harvest may eliminate the problem. Although there are no specific thresholds, as a general guideline if the crop is more than 2 weeks from cutting and 25 to 30 percent of the terminals are damaged, treatment is suggested.

Soybeans
Be sure to watch for defoliators in both full season and double crop soybeans. In full season soybeans, the defoliation drops to 10-15% defoliation at the bloom to pod fill stages. Double crop soybeans cannot handle as much defoliation as full season fields at the pre-bloom or pod-fill stages. In addition to our normal mix of defoliators (i.e. grasshoppers, green cloverworm, and Japanese beetles), be sure to watch for beet armyworm. There are reports of a few fields with beet armyworm in Virginia. Since beet armyworm larvae have been found for the last 3 weeks in pepper and watermelon fields in Sussex County we know it has migrated to our area. Corn earworm larvae can also be found at low levels in full season and a few double crop fields. With the drought stressed corn in our area, the potential for earworm populations may be higher this season.

During the winter season, we discussed the potential for a new insect pest of soybeans, the Kudzu Bug. This insect has been attacking soybeans in Georgia, South Carolina, North Carolina and now a number of counties in southern Virginia. The Delaware Soybean Board has provided us with funding for a survey for this insect pest, So far we have not detected any on soybeans or Kudzu. We will keep you posted on what we find. The following is a link to a webcast by Dr. Jeremy Greene from Clemson University. The webcast contains information on tentative treatment threshold recommendations, expected control with insecticides, the history of the distribution of the insect in the USA, identification of the life stages of the species, and data demonstrating potential yield losses due to Kudzu bug.
http://www.plantmanagementnetwork.org/edcenter/seminars/soybean/kudzu/

With the extended drought conditions in our area, we continue to find significant populations of spider mites in both full season and double crop fields as well as in irrigated fields. In most cases, infestations at this time are field wide, so edge treatments will not be effective. As we have learned in past years, drought will seriously stress plant growth, favor mite development and create plant growth conditions that make it difficult to achieve effective control. Early detection, rotation among available control options and multiple applications are often needed under drought stress conditions. Under high population pressure, a single treatment is often not adequate to kill all the life stages. Mite eggs will not be affected by the initial knockdown/control of adults and nymphs and thus hatch after a few days. The only available materials for spider mite management in soybeans in Delaware are dimethoate, Lorsban (as well as generic chlorpyrifos products), bifenthrin (numerous generics available) and Hero. (Be sure to read all labels before spraying for restrictions and rates). Unfortunately, we do not have a selective miticide labeled for soybeans like we do in vegetable and fruit crops. The following is a summary of what we have seen so far this season as well as a summary of results from past seasons.

Hero and bifenthrin Products – A number of products containing the active ingredient bifenthrin are available for spider mite management in soybeans. Some examples include Brigade, Bifenture, Frenzy and Sniper. In addition, Hero, a combination product including both bifenthrin and zeta-cypermethrin (two pyrethroids) is also available. In many cases, these materials have provided good initial control but a second treatment has been needed in some fields, especially if populations were exploded at the time of treatment and numerous mite eggs were present. Early detection and control is needed as with all of the materials available for mite management in soybeans. In addition, most of the labels for products containing bifenthrin state “do not make applications less than 30 days apart or do not apply more than once every 30 days“. Therefore, you will need to rotate to a material with a different mode of action if a second application is needed.

Dimethoate – In past years, dimethoate has not provided effective spider mite management under drought stress conditions. However, this year we have received reports of fairly good control in some situations but it should be noted that rain was received in those areas. Although dimethoate is the only systemic material available for spider mite management in soybeans it must be absorbed and translocated by the leaf tissues to provide residual action; otherwise, it undergoes rapid photodecomposition from sunlight. This leaf absorption process is greatly reduced in drought-stressed plants that have “shut-down” physiologically. Another important factor that plays a role in the performance of dimethoate is the pH of the water used as the carrier. Many pesticides, especially dimethoate, are subject to breakdown by alkaline hydrolysis. (http://www.ag.ndsu.nodak.edu/aginfo/entomology/entupdates/ICG_08/01_Intro_08.pdf) In alkaline water (high pH), there is a break in certain bonds in the dimethoate molecule, causing two or more new molecules to form. This increases the decomposition rate of the insecticide and can result in poorer than expected field performance. Dimethoate degradation is also accelerated by the mineral content of the water, especially the presence of iron. If a high pH situation exists, you can lower the alkalinity of the water in the spray tank by adding an acid-based buffer. An important consideration is to select a buffering product that lowers the pH to the acid range without causing phytotoxicity. Also, the buffer must be added to the spray tank first, before the addition of dimethoate.
Note – the dimethoate label states it has a “ 7-day reapplication interval. “

Lorsban (chlorpyrifos) – We have seen good initial control of mites with Lorsban and other generic chlorpyrifos products this season. A second application with another material has been needed, especially if populations were exploded at the time of treatment and numerous mite eggs were present. Lorsban (and other generic chlorpyrifos products) can provide good contact control of motile mites when applied in enough water to get good coverage. Since Lorsban is not a systemic product, a second spray of non-chlorpyrifos product may be needed in 5 to 7 days to kill newly hatched mites. The Lorsban label states that: (1) When large numbers of eggs are present, scout the treated area in 3-5 days and if newly hatched nymphs are present, make a follow up application with a non-chlorpyrifos product and (2) do not make a second application of Lorsban 4E or other product containing chlorpyrifos within 14 days of the first application.

So before applying any material, be sure to read the label for rates as well as all restrictions including but not limited to the total number of applications allowed, rotation between materials, minimum number of days required between applications as well as the pre-harvest interval between last application and harvest. Spider mite management is never easy under drought stress conditions. Early detection and multiple applications of materials with different modes of action are often needed to reduce losses from this pest in soybeans. As a reminder, under heavy mite pressure and extended hot, dry weather, it often takes an extended period of free moisture on leaves, high humidity during the day and cool evening temperatures to get an increase in the fungal pathogens that can significantly reduce exploded mite populations.

Agronomic Crop Insects – July 13, 2012

Thursday, July 12th, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Alfalfa
Continue to scout fields on a weekly basis for leafhoppers. It is also time to start watching for defoliators in alfalfa, including grasshoppers, corn earworm, webworms and beet armyworm.

Soybeans
In full season as well as soybeans planted after barley, the major defoliators continue to be Japanese beetles and green cloverworm. We are also starting to see an increase in bean leaf beetles and blister beetles. In double crop soybeans planted behind wheat, grasshoppers continue to be the predominant defoliator present at this time. Remember, at the bloom to pod fill stage in full season soybeans, the defoliation threshold drops to 10-15% defoliation. Double crop soybeans can not handle as much defoliation as full season fields at the pre-bloom or pod-fill stages.

Economic levels of spider mites continue to be found in both irrigated and dry land fields in Kent and Sussex counties. It is important to continue to scout the entire field since hot spots can be found throughout fields and edge treatments may not be effective. As a reminder, under heavy mite pressure and extended hot, dry weather, it often takes extended periods of free moisture on leaves, high humidity during the day and cool evening temperatures to get an increase in the fungal pathogens that can significantly reduce exploded mite populations. If egg populations are high at the time of application, two applications will mostly likely be needed. Be sure to read the labels for use rates and restrictions – there is a limit on the number of applications as well as the time between applications on all of the materials labeled for spider mite control. Lastly, be sure to consult your crop insurance provider regarding their rulings this year regarding the need to make an attempt to control mites under drought stress conditions.