Posts Tagged ‘slugs’

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

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 23rd, 2008

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

Alfalfa
When checking regrowth for damage from weevils, be sure to also consider damage from adults. If economic levels were present before cutting and no spray was applied, both adults and larvae can hold back re-growth. With the cool conditions we have had, there would not have been enough “stubble” heat to control the weevils with a cutting. Potato leafhoppers are now present in fields so be sure to sample on a weekly basis after the first cutting. 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
Slugs continue to be the main pest of concern in many fields. Options to reduce damage and allow plants to grow ahead of the damage include the use of Deadline M-Ps and 30% nitrogen applied at night when the plants are dry (the rate used in past years was 20 gallons/acre of 30% N on corn in the spike to one-leaf stage and the mix was cut 50/50 with water to reduce, not eliminate, plant injury). Also, slugs seem to be most active on the plants between midnight and 3 a.m. so applications of nitrogen have been most effective when applied between those hours. As indicated in past newsletters, the best control with the Deadline M-Ps has been observed when applications were made and there was at least one day of sunny weather after an application. In general slugs stop feeding in 2-3 hours even though it may take the slugs 2-3 days to die. If conditions remain extremely wet, slugs sometimes can absorb enough moisture to compensate for the water lost in mucus production so a second application may be needed. We have also had reports and have seen good results in commercial fields where a potash application was needed and slugs were also present in the field. It has probably been effective due to its high salt index. Remember that when it comes to slug management all of the available control tactics only reduce the slug activity – buying time to enable the crop to outgrow the problem.

In 2003 when we had the last significant problem from slugs, the following was reported by Galen Dively from the University of Maryland regarding his research on slug damage in field corn:
“I conducted a field study several years ago to measure the corn plant’s ability to withstand slug damage. The work was done in a no-till field with closed seed slots and an average of ten slugs per plant at emergence. At the 2-3 leaf stage, individual plants were rated for damage and then flagged for later assessments of seedling mortality and plant growth at 1, 2, and 4 weeks after the initial rating. No controls were applied, so the slug population present at plant emergence was allowed to develop and feed on seedlings after the damage ratings were made. The rating categories included: 1= seedling completely severed at ground level; 2= all leaves consumed except one remaining intact (greater than 75% defoliated); 3= all leaves showing moderate damage, but entire plant intact (25 to 50% defoliated); 4= only one leaf showing damage (less than 25% defoliated); 5= no damage. Approximately 100 plants were rated in each category and the following data were obtained:

Damage Rating

Avg. % Seedling Mortality

Avg. # of leaves

At 1 wk At 2 wks. At 4 wks.
1 48 68 5.1
2 11 17 5.8
3 0 0 6.2
4 0 0 7.6
5 0 0 7.5

“The study showed that a considerable amount of slug injury could be tolerated before plant density and growth is severely affected. Although regrowth delayed the production of leaves, 32% of the severed plants and 83% of the plants that were more than 75% defoliated recovered after 2 weeks from the initial onset of injury. All plants in categories 3 (25 to 50% defoliated) and 4 recovered completely and were not significantly different from undamaged plants with respect to the number of leaves and plant height later in the season. Although individual plant yields were not determined, there were no observable differences in plant or ear size at harvest between damaged and undamaged plants; thus, any yield loss from slug damage is probably directly related to stand reduction.

“Based on this study, populations of five or more slugs around each plant prior to the 3-leaf stage may be economic, especially if injury is heavy, plant growth is slow, and cool, wet conditions prevail. If the weather turns hot and dry, 10 or more slugs per plant may be tolerated if the seedlings reach the 3-leaf stage. Generally, if a heavily infested field reaches the 3-leaf stage without severe seedling mortality, the crop has survived the critical period and should outgrow further slug injury, regardless of the population pressure.”

Small Grains
Fields that were treated with a combination fungicide/insecticide spray and have been re-scouted for insects are still free of insect activity so it appears that those applications are still providing control. However, we continue to find “worms” in barley and wheat fields that were not treated so be sure to check fields as soon as it is dry enough to do a good job scouting. In many cases populations are lower than might be expected with the high trap catches experienced in early May, which indicates that the weather conditions helped to reduce population levels.

Soybeans
As the earliest beans emerge, slugs, bean leaf beetles and grasshoppers can be found feeding on seedling stage plants. After last season, we all know that grasshoppers can be extremely difficult to control and multiple applications will be needed. Unfortunately, the warm winter conditions could result in significant problems again this year so be sure to check for grasshoppers as soon as plants emerge. Early detection and control of small grasshoppers is necessary to achieve control. Numerous products are labeled for grasshopper control including a number of pyrethroids, dimethoate, Furadan (currently under review by EPA for cancellation but FMC Rep says it should be available this year), Lorsban, Orthene 97 and Sevin XLR. As a reminder, OP insecticides (like dimethoate or Lorsban) cannot be combined with SU/ALS herbicides (like Harmony GT). Since other materials may also state restrictions regarding combinations of insecticide and herbicides, you should be sure to check all labels carefully before combining insecticides and herbicides. Combinations of certain formulations, especially emulsifiable concentrates (ECs), can cause significant phytotoxicity.

Slugs – Scouting and Control in Field Corn

Friday, May 2nd, 2008

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

Biology of Slugs
Most slugs pass through a single generation per year. Although they generally overwinter in the egg stage, we can often find juveniles and adults all winter, especially if conditions are warm. Since slugs may live 12 to 15 months and eggs are laid both in the early spring and fall, overlapping generations of adult and juvenile stages may be observed. In the winter, adult slugs may enter a state of hibernation, and in the dry and hot summer conditions they enter a similar inactive state. A combination of one or more of the following factors favors slug outbreaks: no-tillage field crop production practices; development of dense weed cover or addition of organic matter such as manure; mild winters which increase the number of overwintering stages, especially adult slugs; prolonged periods of favorable temperatures (63 to 68°F) combined with evenly distributed rainfall that maintains soil moisture at 75% saturation; high pH (6.3 – 6.7); over fertilization with nitrogen and cool growing conditions which delay crop development and extend the period of susceptibility of the crop to slug injury.

Scouting for Slugs
You can still identify fields with the potential for problems before planting by using a shingle or covered pit to provide a humid, sheltered hiding place for slugs. Slugs tend to congregate in large numbers in these shelters. As a rule of thumb, you can expect problems in a field if you find one to five slugs per trap. Once a field is planted, you should examine fields with a potential for damage on weekly basis. Slug damage will appear as a shredding of the leaves since they feed by grating away the surface of the plant tissue. The presence of “slime trails” can also be used to distinguish slug injury. Look for slugs under dirt clods and surface trash around 5 plants in 10 locations in a field. Since slugs are nocturnal, sampling should be done in the evening or when weather is cloudy. As a general guideline, a treatment may be needed if conditions are favorable for slug development and you find 5 or more slugs around each plant from the spike to 3-leaf stage.

Controls
Management options are still limited to the use of baits and cultural practices. If a number of factors are present which favor slug development, then a combination of cultural practices and baits may be needed. Cultural practices, including the use of “pop-up” fertilizer and trash whippers to remove residue over the seed furrow, can help corn grow ahead of the damage. When populations were extremely heavy in the spring of 2003, good results were obtained with Deadline MPs (metaldehyde bait). The label states 10 – 40 lbs per acre (http://www.cdms.net/LDat/ld7CL000.pdf ). We saw good results with 10 lbs. per acre broadcast applied with a cyclone spreader if the spreader was calibrated so you are getting at least 5 pellets per square foot. Also, the best results have been observed when applications were made and there was at least one day of sunny weather after an application. In general slugs stop feeding in 2-3 hours even though they may take 2-3 days to die. If conditions remain extremely wet, slugs sometimes can absorb enough moisture to compensate for the water lost in mucus production so a second application may be needed. Most baits, as well as cultural practices, only reduce the slug activity – buying time to enable the crop to outgrow the problem.