Posts Tagged ‘grass sawfly’

Agronomic Crop Insects – April 22, 2011

Friday, April 22nd, 2011

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

Alfalfa
Continue to scout fields for both alfalfa weevil and pea aphids. Economic levels of both can be found in alfalfa fields at this time. As a general guideline, you should consider a treatment in alfalfa less than 10 inches tall if you find 40-50 aphids per stem. The treatment threshold for alfalfa 10 inches or taller in height is 75- 100 per stem. Although beneficial insects can help to crash aphid populations, cooler temperatures will slow their activity. As a general rule, you need one beneficial insect per every 50-100 aphids to help crash populations. As soon as temperatures increase, we will start to see a significant increase in feeding damage from alfalfa weevil. As alfalfa approaches harvest, the decision to cut instead of treat may be considered. However, this option should only be used if you plan to cut shortly after you find an economic threshold level since damage can occur quickly. Cutting should only be considered as a management option if you can cut within 3- 5 days of finding an economic level. Also, the effectiveness of using cutting as a management strategy is affected by temperatures after cutting. If the temperature remain cool, it has not always been effective. Since you need “stubble heat” to get control. As you get close to harvest, be sure to check labels carefully for time between application and harvest.

Field Corn
As soon plants emerge, be sure to check for cutworm feeding, even if an at-planting insecticide or a Bt corn was used for cutworm control. The wet soil conditions this spring have resulted in a higher level of grey garden slugs being found under residue in no-till fields. Although we see more problems in seedling corn when temperatures remain cooler and soil remains wet, it is generally during the warmer days of April when we start to see egg hatch. You will need to sift through previous crop residue and look at the soil surface for slugs. We are generally finding eggs and adults at this time; however we have started to see the first juveniles as well. The eggs, which are clear and about half the size of a BB, are often found in clusters within crop residue or at the soil surface. Although no thresholds are available, past experience in the Mid-Atlantic has indicated that pre-plant levels of five or more grey garden slugs per square foot can indicate the potential for a problem. In 2010, DuPont issued a 2ee recommendation for Lannate LV for slug management (http://www.cdms.net/LDat/ld183004.pdf); however, we have limited experience with the use of Lannate for slug management. Most of our experience has been with the use of a broadcast application of Deadline M-Ps at the low end of the labeled rate (http://www.cdms.net/LDat/ld7CL003.pdf). For more information on slug biology, sampling and management, please refer to the following fact sheet from Ohio State University: http://ohioline.osu.edu/ent-fact/pdf/0020.pdf.

SmartStax Approved for Refuge-In-Bag
Here is a summary of information on recent federal labeling of refuge-in-the-bag (RIB) from the Ohio State C.O.R.N newsletter (Ron Hammond, Extension Entomologist). Commercialization is pending individual state authorizations and notifications, as required.

“Two SmartStax corn products having the refuge-in-the-bag (RIB) concept have received registration from the U.S. Environmental Protection Agency, Genuity SmartStax RIB Complete by Monsanto Company and REFUGE ADVANCEDpowered by SmartStax by Dow AgroSciences. Both of these products are a blend of 95 percent SmartStax corn seed and 5 percent refuge (non-Bt) seed that farmers can plant across their entire field. This means farmers who plant these products no longer need to plant a separate, structured refuge for above-or below-ground pests in the Corn Belt. These new products are the outcome of collaboration between Monsanto and Dow AgroSciences, with both expecting a full commercial launch with broad lineups of hybrids for sale for 2012 planting.”

Small Grains
Although aphid population remain low, weather conditions favoring quick increases in populations include a combination of cool temperatures followed by a quick increase in temperatures. Although beneficial insects can help to crash aphid populations, cooler temperatures will slow their activity. As a general rule, you need one beneficial insect per every 50-100 aphids to help crash populations. Since barley heads are starting to emerge in some locations, be sure to watch for the movement of aphids into grain heads. In many cases, beneficial activity is still not high enough to take care of populations that can move from the lower canopy of the plants into the grain heads. http://ag.udel.edu/extension/IPM/ExtensionFactSheets/AphidControlinSmallGrainIPM-4.pdf

Cereal leaf populations still remain relatively low but we can now find the first larvae in fields. Refer to our factsheet (http://ag.udel.edu/extension/IPM/ExtensionFactSheets/CerealLeafBeetleFactSheetIPM-5.pdf) as well as the Agronomic Crop Insects article in WCU 19:2 for sampling and treatment guidelines.

Once grain heads have emerged, you should also begin sampling small grains for grass sawfly and armyworm larvae. Although we can see economic damage from local overwintering armyworm populations, we often see significant outbreaks in years when moths coming from the South migrate to our area. Reports from trapping programs in Kentucky are indicating that trap catches for 2011 appear to be following their 2006 & 2008 outbreak levels – so be sure to begin checking for small larvae. http://www.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN1264.pdf

Remember, armyworm larvae are nocturnal so look for larvae at the base of the plants during the day. As a general guideline, a treatment should be considered if you find one armyworm per foot of row for barley and 1-2 per foot of row for wheat. The first small sawflies have been found by consultants in wheat and barley in Kent and Sussex counties. Since sawflies feed on the plants during the day, small sawfly larvae can often be detected early using a sweep net. However, there is no threshold for sweep net samples. Once sawfly larvae are detected, sample for larvae in 5 foot of row innerspace in 5-10 locations in a field to make a treatment decision. You will need to shake the plants to dislodge sawfly larvae that feed on the plants during the day. As a guideline, a treatment should be applied when you find 2 larvae per 5 foot of row innerspace or 0.4 larvae per foot of row. If armyworms and sawflies are present in the same field, the threshold for each should be reduced by one-half. The higher rates of insecticides are needed for grass sawfly control. http://ag.udel.edu/extension/IPM/ExtensionFactSheets/SawflyandArmywormIPM-6.pdf

 

Agronomic Crop Insects – April 30, 2010

Thursday, April 29th, 2010

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

Alfalfa
If economic levels of alfalfa weevil were present before harvest and you decide to cut instead of spray, be sure to check fields within one week of cutting for damage to the regrowth. If temperatures remain cool after cutting, there is often not enough “stubble heat” to control populations with early cutting. In some cases, damage to re-growth can be significant. A stubble treatment will be needed if you find 2 or more weevils per stem and the population levels remain steady.

Small Grains
During the past week, there has been a significant increase in populations of cereal leaf beetle larvae, especially in areas where adult egg laying has been abundant over the last few weeks. In many cases, larvae were very small (about the size of a pin-head) early in the week; however, they will quickly increase in size with the predicted warm temperatures. In addition, they can be found throughout the plant canopy so you need to look at the entire plant when sampling. Damage can occur quickly under these conditions so be sure to scout carefully for cereal leaf beetle larvae. The treatment threshold is 25 eggs and/or small larvae total per 100 tillers.

With the predicted warmer temperatures, we will also see an increase in true armyworm catches. Although true armyworms overwinter in our area, we can also get migrant moths from the South. Therefore, be sure to scout all small grains for armyworms at this time. Remember, on barley, head clipping can occur in a relatively short time. As a general guideline, the threshold for armyworms in barley is one per foot of row and for wheat one-two per foot of row.

In addition to armyworms, do not forget to watch for sawflies since larvae can be found in fields throughout the state. As a review, adult sawflies generally emerge in early April and begin to lay eggs in the leaf margins of small grains. Most egg laying is complete by early May but can be delayed by cooler temperatures. The first small larvae generally feed on the lower leaf blades and larval development takes approximately 21-30 days. Barley and wheat are both damaged by sawflies; however, during years of high population pressure, barley may experience more damage. Sawfly larvae prefer to feed on the stems and can be more damaging than armyworms. Stem clipping often occurs before leaf feeding is complete and/or the grain reaches physiological maturity. Since sawflies can clip heads quickly, be sure to scout carefully for larvae and watch closely for clipped heads. As a guideline, a treatment should be applied for sawflies when you find 2 larvae per 5 foot of row innerspace or 0.4 larvae per foot of row. However, remember if the number of clipped heads is twice the worm count for sawflies then it may be too late to treat for them.

Since aphids feeding in the heads of small grains can result in a loss in test weight, be sure to watch for movement of aphids into the grain heads. As a general guideline, a treatment should be considered if you find 20 aphids per head and beneficial insect activity is low. You need at least one beneficial insect per every 50-100 aphids to help crash populations.

Lastly, before treating for any insect be sure to check the days between last application and harvest when selecting a spray material.

Agronomic Crop Insects

Thursday, April 22nd, 2010

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

Alfalfa
Continue to scout fields for both alfalfa weevil and pea aphids. Economic levels of both can be found in alfalfa fields at this time. As a general guideline, you should consider a treatment in alfalfa less than 10 inches tall if you find 40-50 aphids per stem. The treatment threshold for alfalfa 10 inches or taller in height is 75- 100 per stem. Although beneficial insects can help to crash aphid populations, cooler temperatures will slow their activity. As a general rule, you need one beneficial insect per every 50-100 aphids to help crash populations. As soon as temperatures increase, we will start to see a significant increase in feeding damage from alfalfa weevil. As alfalfa approaches harvest, the decision to cut instead of treat may be considered. However, this option should only be used if you plan to cut shortly after you find an economic threshold level since damage can occur quickly. Cutting should only be considered as a management option if you can cut within 3- 5 days of finding an economic level. As you get close to harvest, be sure to check labels carefully for time between application and harvest.

Field Corn
As soon plants emerge, be sure to check for cutworm feeding, even if an at planting insecticide was used for cutworm control. A combination of wet conditions and the extended heavy snow cover has resulted in a higher level of slugs being found under residue in no-till fields. Although no true thresholds are available, levels of 5 or more slugs per square foot have indicated the potential for a problem from slugs.

Small Grains
Although aphid population remain low, a combination of cool temperatures followed by a quick increase in temperatures can result in a quick increase in aphid populations. In research done in VA in past years they found that small grains can tolerate a lot of feeding in the lower canopy. Since we are past the time of barley yellow dwarf transmission (fall transmission is the most important), the next important time to consider aphid management in small grains is at grain head emergence. Since aphids feeding in the heads of small grains can result in a loss in test weight, it is important to look for aphids as soon as the grain heads emerge. As a general guideline, a treatment should be considered if you find 20 aphids per head and beneficial insect activity is low. Although beneficial insects can help to crash aphid populations, cooler temperatures will slow their activity. As a general rule, you need one beneficial insect per every 50-100 aphids to help crash populations. Since barley heads have emerged, be sure to watch for the movement of aphids into grain heads. In many cases, beneficial activity is still not high enough to take care of populations moving from the lower canopy of the plants into the grain heads.

Once grain heads have emerged, you should also begin sampling small grains for grass sawfly and armyworm larvae. Remember, armyworm larvae are nocturnal so look for larvae at the base of the plants during the day. As a general guideline, a treatment should be considered if you find one armyworm per foot of row for barley and 1-2 per foot of row for wheat. The first small sawflies have been found in wheat and barley in Kent and Sussex counties. Since sawflies feed on the plants during the day, small sawfly larvae can often be detected early using a sweep net. However, there is no threshold for sweep net samples. Once sawfly larvae are detected, sample for larvae in 5 foot of row innerspace in 5-10 locations in a field to make a treatment decision. You will need to shake the plants to dislodge sawfly larvae that feed on the plants during the day. As a guideline, a treatment should be applied when you find 2 larvae per 5 foot of row innerspace or 0.4 larvae per foot of row. If armyworms and sawflies are present in the same field, the threshold for each should be reduced by one-half.

Agronomic Crop Insects

Friday, May 16th, 2008

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

Alfalfa
In addition to checking for weevils feeding on re-growth, be sure to check fields for leafhoppers within one week of cutting. You will also need to carefully sample all spring planted fields since they are very susceptible to damage. Once the damage is found, yield loss has already occurred. The treatment thresholds are 20 per 100 sweeps on alfalfa 3 inches or less in height, 50 per 100 sweeps in 4-6 inch tall alfalfa and 100 per 100 sweeps in 7-11 inch tall alfalfa.

Field Corn
Continue to sample all fields for cutworms, slugs and true armyworm. Be sure to sample all fields through the 5-leaf stage for cutworm damage. As a general guideline, a treatment should be considered if you find 3% cut plants or 10% leaf feeding. If cutworms are feeding below the soil surface, it will be important to treat as late in the day as possible, direct sprays to the base of the plants and use at least 30 gallons of water per acre. You should also sample no-till fields for true armyworms, especially where a grass cover or volunteer small grains were burned down at planting. As a general guideline, a treatment may be needed for armyworms if 25% of the plants are infested with larvae less than one inch long. As small grains dry down, you should also watch for armyworms moving from small grains into adjacent corn fields.

Small Grains
Continue to scout fields for armyworms and sawflies, as well as aphids feeding in the heads of small grains. We are starting to see an increase in the number of armyworm larvae found in untreated wheat and barley fields. The following are a few things to remember about the biology of armyworms and the damage they can cause in small grains:
● Young larvae (less than ½ inch long) generally feed on the upper leaf surface.

● Larger larvae can feed heavily on the leaf blades and weeds.

● The last instar (1.5 inches long and greater) will consume 80 percent of all the plant material eaten during their larval development. This stage lasts six to eight days before moving into the soil to pupate.

● Heavy defoliation of the flag level can result in significant economic loss.

● Unlike the sawfly, armyworms generally begin head clipping when all vegetation is consumed and the last succulent part of the plant is the stem just below the grain head. They also can clip the heads of barley faster than wheat.

● Larvae can feed on the kernel tips of wheat, resulting in premature ripening and lower test weight. If fields were sprayed early, be sure to check fields to be sure that you do not miss an infestation.

Soybeans
Throughout the month of May, seed corn maggot will continue to be a potential problem in no-till soybeans as well as conventional soybeans where a cover crop is plowed under before planting or where manure was applied. All of these situations are attractive to egg laying flies. Control options are limited to the commercial applied seed treatments, Cruiser/Cruiser MAXX and Gaucho (for use in commercial seed treaters only) and one hopper box material containing permethrin (http://www.tracechemicals.com/trace/labels/KernelGuardSupremelabel.pdf ). Labels state early season protection against injury by seed corn maggot.

As the earliest beans emerge, be sure to watch for slugs, bean leaf beetles and grasshoppers. We have seen all three pests feeding on seedling stage beans.

On the earliest emerged fields, be sure to watch for bean leaf beetle adults feeding on the cotyledons and first true leaves. In recent years, bean leaf beetle populations have been heavier in the Mid-Atlantic and we can find damage on the earliest planted beans. Damage appears as scooped out pits on the cotyledons and leaf feeding appears as distinctive, almost circular holes, which are scattered over the leaf. Refer to the following link for pictures of adults and damage (http://www.ent.iastate.edu/imagegal/coleoptera/beanlb/). Even though the feeding by first-generation beetles on soybean leaves has seldom resulted in economic yield losses (except if virus is vectored), fields should be scouted carefully to assess the damage. In the Midwest, this beetle vectors bean pod mottle virus. The presence of bean pod mottle virus was confirmed for the first time in Delaware in 2007 by Bob Mulrooney. The second-generation feeding on pods in late summer could cause significant damage. This generation would also be the generation to vector virus next spring. There are numerous treatment guidelines available. However, as a general guideline, a treatment may be needed if you observe a 20 – 25% stand reduction and/or 2 beetles per plant from cotyledon to the second trifoliate stages. The Iowa State economic threshold for cotyledon stage is four beetles per plant. Once plants reach the V1 and V2 stages, their thresholds increase to 6.2 (V1 stage) and 9.8 (V2 stage) beetles/plant. These treatment thresholds should be reduced if virus is present or you suspected virus the previous season.

As far as the commercial applied seed treatments (Cruiser and Gaucho), both materials are labeled to provide early protection against injury from bean leaf beetle. However, these seed treatments will not limit later population growth in mid to late summer. For growers who choose to control overwintering bean leaf beetles to limit virus transmission, information from the Midwest indicated that an early season foliar spray after plant emergence, followed by a second spray in July for the first generation beetles might be tried. Because seed treatments will offer control of the overwintered beetles and reduce feeding injury, growers might want to use seed treatments to replace the early season foliar spray. Currently, we do not have all the answers as to whether controlling the overwintered beetles with seed treatments will reduce virus transmission. Data from the Midwest is variable – some say that the use of seed treatments may be one part of an overall effective pest management program, while other data suggests that this approach might not give economic control of the virus. We are again evaluating seed treatments this year in areas of the state where bean leaf beetle populations were high in 2007 and bean pod mottle virus was found.

Small grasshoppers can be found in full season no-till plantings. In general, the treatment threshold for grasshoppers is 1 per sweep and 30% defoliation. Early detection of small grasshoppers and multiple applications are often needed for grasshopper control.

True Armyworms and Grass Sawfly

Wednesday, March 26th, 2008

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

Each year economic levels of true armyworm and grass sawfly can be found in fields throughout the state. Field scouting is the only way to determine if economic levels are present in your fields. The following information is a review of the biology and life history of grass sawfly and true armyworm in wheat.

Grass sawfly adults emerge in early April and begin to lay eggs in the leaf margins of small grains. Most egg-laying is complete by early May. The first larvae can be found by late April feeding on the lower leaf blades. Mature larvae can be distinguished by their solid green color, amber head with a brown band and many legs. Larval development takes approximately 21-30 days. By mid-June, larvae burrow into the ground and begin a period of summer diapause (hibernation). Sawfly larvae prefer to feed on the stems and are potentially more damaging than armyworms. Larvae begin to climb and feed on stems when the larvae are half grown and the grain is in the tiller to head stage. Stem clipping often occurs before leaf feeding is complete and/or the grain reaches physiological maturity. Head clipping often peaks before peak armyworm damage. (more…)