Posts Tagged ‘winter grain mite’

Agronomic Crop Insects – April 1, 2011

Friday, April 1st, 2011

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

Alfalfa
Alfalfa Weevil:
We are starting to see the first hatch of alfalfa weevil eggs. As soon as the weather begins to warm up, you should begin to sample for larvae on a weekly basis. Look for small larvae feeding in the tips of plants producing a round, pinhole type of feeding. Once you detect tip feeding, a full field sample should be taken. The most accurate way to time an application is to sample stems and determine the number of weevils per stem. A minimum of 30 stems should be collected per field and placed top first in a bucket to dislodge larvae from the tips. Then count the number of weevils per stem. The following thresholds, based on the height of the alfalfa, should be used as a guideline when making a treatment decision: up to 11 inches tall – 0.7 per stem; 12 inches tall – 1.0 per stem; 13 – 15 inches tall – 1.5 per stem; 16 inches tall – 2.0 per stem; and 17 – 18 inches tall – 2.5 per stem. Numerous pyrethroids are now labeled for alfalfa weevil including Baythroid XL, Mustang MAX, Proaxis, Warrior II and numerous generic pyrethroids. Imidan, Lorsban, Lannate and Steward are also labeled for alfalfa weevil control. Be sure to check all labels for rates, restrictions and days to harvest before application. The following is a link to our recently updated fact sheet including pictures of life stages and damage.  http://ag.udel.edu/extension/IPM/ExtensionFactSheets/AlphalfaWeevilIPM-1.pdf.

Timothy
Cereal Rust Mites:
Since spring green-up is underway, be sure to sample fields for cereal rust mite activity. Mites can be found in fields at this time. These mites are very small, so the use of a 20x-magnifying lens may be helpful. If rust mites become a problem, Sevin XLR Plus is still the only labeled, effective material: http://www.cdms.net/LDat/ld332013.pdf . Be sure to read the label for information on the number of applications per season as well as the days to harvest. For effective rust mite control, the use of the higher labeled rate and at least 25 gal/A of carrier to get good coverage of leaf surfaces generally results in better control. The following is a link to new fact sheet including pictures of mites and damage: http://ag.udel.edu/extension/IPM/ExtensionFactSheets/CerealRustMiteIPM-9.pdf.

Wheat
Cereal Leaf Beetle:
It is time to begin sampling fields for cereal leaf beetle activity. We are starting to find evidence of adult feeding, so fields should now be scouted for egg masses. The threshold for cereal leaf beetle includes sampling for eggs, especially in high management wheat fields or in fields with historical problems. The eggs are elliptical, about 1/32 inch long, yellow in color when first laid, changing to a burnt orange prior to hatching. The following is a link to our recently updated fact sheet including pictures of life stages and damage: http://ag.udel.edu/extension/IPM/ExtensionFactSheets/CerealLeafBeetleFactSheetIPM-5.pdf.

Generally, eggs are laid singly or in small scattered groups (end-to-end) on the upper leaf surface and parallel to the leaf veins. Cereal leaf beetle larvae are brown to black, range in size from 1/32 to ¼ inch long, and eat streaks of tissue from the upper leaf surface. Since cereal leaf beetle populations are often unevenly distributed within the field, it is important to carefully sample fields so that you do not over or under estimate a potential problem. Eggs and small larvae should be sampled by examining 10 tillers from 10 evenly spaced locations in the field while avoiding field edges. This will result in 100 tillers (stems) per field being examined. Eggs and larvae may be found on leaves near the ground so careful examination is critical. You should also check stems at random while walking through a major portion of the field and sampling 100 stems. The treatment threshold is 25 or more eggs and/or small larvae per 100 tillers. If you are using this threshold, it is important that you wait until at least 50% are in the larval stage (i.e. after 50% egg hatch).

Winter Grain Mites: With the recent cooler weather, consultants are starting to report an increase in winter grain mite populations, especially in no-till wheat planted into corn stubble. Temperature and moisture are the most important factors influencing mite development and abundance. Cool, rather than warm, temperatures favor their development. Egg laying is heaviest between 50° and 60°F and the optimum conditions for hatching are between 44° and 55°F. Mite activity in the spring drops rapidly and the eggs fail to hatch when the daily temperature exceeds 75°F. The larvae as well as the adults feed higher up on the plants at night or on cloudy days. Heavily infested fields appear grayish or silvery, a result of the removal of plant chlorophyll by mite feeding. When high infestations feed on the plants for several days, the tips of the leaves exhibit a scorched appearance and then turn brown, and the entire plant may die. These mites do not cause the yellowing characteristic of spider mite feeding. Many of the infested plants do not die, but become stunted and produce little forage or grain; damage on young plants, however, is more severe than on large, healthy ones. Damage may also be greater in plants stressed by nutrient deficiencies or drought conditions. There are two types of damage to the small grain: (a) reduced amount of forage throughout the winter and (b) reduced yields of grain in the spring and summer. The following is a link to our recently updated fact sheet including pictures of mites: http://ag.udel.edu/extension/IPM/ExtensionFactSheets/WinterGrainMitesIPM-8.pdf.

The most effective scouting method is to use a 10x hand lens, checking both plant foliage and crop residue on the soil surface for the presence of immature and adult mites. A sweep net may also be effective in determining if mites are present. The best time to scout is early in the morning and at dusk on calm days because the mites will seek refuge during the day in the top 4 or 5 inches of the soil profile to avoid the sunlight. On cool, overcast days, they may be observed actively feeding on plant foliage throughout the day.

No economic thresholds have been developed for WGM in small grain fields. However, as a general rule of thumb, if plants exhibit symptoms of damage, weather conditions are favorable and several mites per plant are found, a chemical control may be necessary to prevent or reduce yield loss. If populations are small and the plants show no feeding injury or if populations and damage symptoms are isolated, the field should be scouted more frequently to insure yield losses are kept at a minimum.

Agronomic Crop Insects

Thursday, April 8th, 2010

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

Alfalfa
Be sure to watch for economic levels of alfalfa weevil and pea aphids. When sampling for aphids and weevils, collect a minimum of 30 random stems throughout a field and place them top first in a white bucket. For aphids, you want to count the number present per plant as well as any that have dislodged from the stem into the bucket. 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. For alfalfa weevil, you will also want to record the number of weevil larvae per stem. The following thresholds, based on the height of the alfalfa, should be used as a guideline when making a treatment decision: up to 11 inches tall – 0.7 per stem; 12 inches tall – 1.0 per stem; 13 – 15 inches tall – 1.5 per stem; 16 inches tall – 2.0 per stem and 17 – 18 inches tall – 2.5 per stem.

Wheat
Low levels of aphids and cereal leaf beetle adults can be found in fields throughout the state. Since we are past the prime time for 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 cereal leaf beetle populations are often unevenly distributed within the field, it is important to carefully sample fields so that you do not over or under estimate a potential problem. Eggs and small larvae should be sampled by examining 10 tillers from 10 evenly spaced locations in the field while avoiding field edges. This will result in 100 tillers (stems) per field being examined. Eggs and larvae may be found on leaves near the ground so careful examination is critical. You should also check stems at random while walking through a major portion of the field and sampling 100 stems. The treatment threshold is 25 or more eggs and/or small larvae per 100 tillers. If you are using this threshold, it is important that you wait until at least 50% are in the larval stage (i.e. after 50% egg hatch). You will also want to access the Virginia AG Pest Advisory http://www.sripmc.org/Virginia/ for a good article entitled Is Wheat at Greater Risk to Cereal Leaf Beetle?

We are also finding low levels of winter grain mites in no-till wheat fields. This is a cool weather mite so be sure to watch fields for this pest, especially with the predicted cooler temperatures for next week. The following is an overview of this pest written by Dr. Ames Herbert from Virginia Tech: “Winter grain mites attack small grains, including wheat, barley, and oats. The mite also infests and damages legumes, vegetables, ornamental flowers, cotton, peanuts, and various weeds. Adult mites are about 1 mm long, black, with red legs and are fast moving. They quickly run to ground cover when you approach plants. As the name implies, they are winter pests. There are two generations per year. The first develops from over summering eggs. Development begins after the onset of favorable temperature and moisture conditions in late September and October with populations peaking in December and January. The second generation develops from eggs laid by the first generation reaching maximum infestation density in March and April. Populations then decrease as temperatures exceed the range of tolerance. The females of this generation lay aestivating or over summering eggs. Temperature and moisture are the most important factors influencing mite development and abundance. Cool rather than warm temperatures favor their development. Egg laying is heaviest between 50° and 60°F; the optimum conditions for hatching are between 44° and 55°F. When temperatures drop below or rise above these ranges, the mites stop feeding and descend to the ground or burrow into the soil. Mite activity in the spring drops rapidly and the eggs fail to hatch when the daily temperature exceeds 75°F. Aestivating (over summering resting stage) eggs do not hatch in the fall until rains provide adequate moisture. On hot, dry days it may be necessary to dig into the soil to a depth of four or five inches to find mites. The mites are not harmed by short periods of sleet or ice cover or by ground frozen to a depth of several inches. The larvae become very active soon after hatching and begin to feed on the sheath leaves or tender shoots near the ground. The larvae as well as the adults feed higher up on the plants at night or on cloudy days. As the sun rises, the mites descend the plants and seek protection during the hot part of the day on the moist soil surface under foliage. If the soil is dry and there is little foliage cover, they dig into the soil in search of moisture and cooler temperatures. At sunset and thereafter the plants become covered with feeding mites where, with the aid of a searchlight, they can be observed feeding at all hours of the night. Dispersion from field to field may occur by transportation of aestivating eggs or mites on grain stubble or leaves, on soil adhering to implements that are moved about, or on forage or straw carried from infested fields in livestock feeding operations. Aestivating eggs may also be transported on debris by wind, and local distribution may occur by adult migration. Such migrations to grain fields may take place from fencerows or other uncultivated areas. Heavily infested fields appear grayish or silvery, a result of the removal of plant chlorophyll by mite feeding. When high infestations feed on the plants for several days, the tips of the leaves exhibit a scorched appearance and then turn brown, and the entire plant may die. These mites do not cause the yellowing characteristic of spider mite feeding. Many of the infested plants do not die, but become stunted and produce little forage or grain; damage on young plants, however, is more severe than on large, healthy ones. Damage may also be greater in plants stressed by nutrient deficiencies or drought conditions. There are two types of damage to the small grains, namely, reduced amount of forage throughout the winter and reduced yields of grain in the spring and summer. Cropping practices have a marked effect upon the occurrence and damage caused by the winter grain mite. Injury by this mite may be prevented by crop rotation, that is, by not planting small grains more than two years in succession.”

Agronomic Crop Insects

Friday, April 10th, 2009

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

Alfalfa
Be sure to watch for economic levels of alfalfa weevil and pea aphids. When sampling for aphids and weevils, collect a minimum of 30 random stems throughout a field and place them top first in a white bucket. For aphids, you want to count the number present per plant as well as any that have dislodged from the stem into the bucket. In seedling stage alfalfa, a treatment should be considered if you find 5 aphids per stem. 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, the cooler temperatures have slowed their activity. As a general rule, you need one beneficial insect per every 50-100 aphids to help crash populations. For alfalfa weevil, you will also want to record the number of weevil larvae per stem. The following thresholds, based on the height of the alfalfa, should be used as a guideline when making a treatment decision: up to 11 inches tall – 0.7 per stem; 12 inches tall – 1.0 per stem; 13 – 15 inches tall – 1.5 per stem; 16 inches tall – 2.0 per stem; 17 – 18 inches tall – 2.5 per stem.

Wheat
Low levels of aphids and cereal leaf beetle adults can be found in fields throughout the state. Since we are past the prime 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 cereal leaf beetle populations are often unevenly distributed within the field, it is important to carefully sample fields so that you do not over or under estimate a potential problem. Eggs and small larvae should be sampled by examining 10 tillers from 10 evenly spaced locations in the field while avoiding field edges. This will result in 100 tillers (stems) per field being examined. Eggs and larvae may be found on leaves near the ground so careful examination is critical. You should also check stems at random while walking through a major portion of the field and sampling 100 stems. The treatment threshold is 25 or more eggs and/or small larvae per 100 tillers. If you are using this threshold, it is important that you wait until at least 50% are in the larval stage (i.e. after 50% egg hatch).

We are also finding relatively low levels of winter grain mites again, especially in no-till wheat fields. We have also heard of a few fields that have been sprayed. This is a cool weather mite so be sure to watch fields for this pest. The following is an overview of this pest including pest identification, biology/life history and management options written by Dr. Ames Herbert from Virginia Tech.

“Winter grain mites attack small grains, including wheat, barley, and oats. Other hosts include grasses, especially bluegrass, bentgrass, ryegrass, and fescue. The mite also infests and damages legumes, vegetables, ornamental flowers, cotton, peanuts, and various weeds. Adult mites are about 1 mm long, black, with red legs and are fast moving. They quickly run to ground cover when you approach plants.

“As the name implies, they are winter pests. There are two generations per year. The first develops from over summering eggs. Development begins after the onset of favorable temperature and moisture conditions in late September and October with populations peaking in December and January. The second generation develops from eggs laid by the first generation reaching maximum infestation density in March and April. Populations then decrease as temperatures exceed the range of tolerance. The females of this generation lay aestivating or over summering eggs.

“Temperature and moisture are the most important factors influencing mite development and abundance. Cool rather than warm temperatures favor their development. Egg laying is heaviest between 50° and 60°F; the optimum conditions for hatching are between 44° and 55°F. When temperatures drop below or rise above these ranges, the mites stop feeding and descend to the ground or burrow into the soil. Mite activity in the spring drops rapidly and the eggs fail to hatch when the daily temperature exceeds 75°F. Aestivating (over summering resting stage) eggs do not hatch in the fall until rains provide adequate moisture. On hot, dry days it may be necessary to dig into the soil to a depth of four or five inches to find mites. The mites are not harmed by short periods of sleet or ice cover or by ground frozen to a depth of several inches.

“The larvae become very active soon after hatching and begin to feed on the sheath leaves or tender shoots near the ground. The larvae as well as the adults feed higher up on the plants at night or on cloudy days. As the sun rises, the mites descend the plants and seek protection during the hot part of the day on the moist soil surface under foliage. If the soil is dry and there is little foliage cover, they dig into the soil in search of moisture and cooler temperatures. At sunset and thereafter the plants become covered with feeding mites where, with the aid of a searchlight, they can be observed feeding at all hours of the night.

“Dispersion from field to field may occur by transportation of aestivating eggs or mites on grain stubble or leaves, on soil adhering to implements that are moved about, or on forage or straw carried from infested fields in livestock feeding operations. Aestivating eggs may also be transported on debris by wind, and local distribution may occur by adult migration. Such migrations to grain fields may take place from fencerows or other uncultivated areas.

“Heavily infested fields appear grayish or silvery, a result of the removal of plant chlorophyll by mite feeding. When high infestations feed on the plants for several days, the tips of the leaves exhibit a scorched appearance and then turn brown, and the entire plant may die. These mites do not cause the yellowing characteristic of spider mite feeding. Many of the infested plants do not die, but become stunted and produce little forage or grain; damage on young plants, however, is more severe than on large, healthy ones. Damage may also be greater in plants stressed by nutrient deficiencies or drought conditions. There are two types of damage to the small grains, namely, reduced amount of forage throughout the winter and reduced yields of grain in the spring and summer. Cropping practices have a marked effect upon the occurrence and damage caused by the winter grain mite. Injury by this mite may be prevented by crop rotation, that is, by not planting small grains more than two years in succession.”

Although we have no research data in Delaware and limited experience with winter grain mite control in commercial fields, materials labeled for other insects on wheat only that appeared to provide control in 2008 on the Delmarva are the pyrethroids (Warrior II, Mustang MAX) and certain organophosphates (dimethoate). NOTE – only Warrior II is also labeled on barley.

Scout Small Grains for Aphids, Winter Grain Mites and Cereal Leaf Beetle

Friday, March 28th, 2008

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

Recently we are receiving reports of high levels of aphids in barley and wheat fields. The fluctuating temperatures as well as continued dry conditions have been favorable for aphids. As indicated in a previous newsletter, cool, dry conditions generally favor spring outbreaks of aphids. This type of weather allows the aphids to survive and reproduce. Although natural enemies can keep aphids under control, cool dry weather in the spring often allows aphids to reproduce rapidly whereas their natural enemies reproduce slowly. Beneficial insects that attack aphids reproduce slowly at temperatures below 65°F, whereas aphids can rapidly increase when temperatures exceed 50°F. A number of insecticides are labeled for aphid control in wheat including: Baythroid, Baythroid XL, Dimethoate 4E, Lannate LV, Mustang MAX, Penncap-M, Proaxis, and Warrior. Materials labeled for aphid control in barley include Lannate, Penncap-M and Warrior. Check the labels for restrictions and harvest intervals. The recent Virginia Ag Pest Advisory from Ames Herbert indicates that they are hearing of many wheat (and some barley) fields with unusually high aphid numbers. Please use the following link for his comments on aphid management in wheat. (http://www.sripmc.org/Virginia/View.cfm?lngNewsID=487)

We continue to receive report of wheat fields with damage from winter grain mites. Remember, this mite is favored by cooler conditions. No thresholds are available for this mite pest. As indicated in the most recent Virginia Ag Pest Advisory written by Tom Kuhar, these mites have been found almost exclusively in no-till wheat situations. Very little is known about this sporadic pest; however, experience in Virginia this season indicates that that high densities of these mites can significantly affect plant vigor and growth. Although we have no experience with winter grain mite control in wheat, materials that have appeared to provide control in areas to our south include the pyrethroids (Warrior, Mustang MAX) and certain organophosphates (dimethoate). Note that dimethoate may not be effective when temperatures are below 60°F. Be sure to follow the rates and usage restrictions on the labels.

As temperatures increase in April, be sure to look for cereal leaf beetle adults, especially along field edges that border woods or in protected areas. Adult beetles feed along the veins of grain leaves leaving characteristic narrow linear holes parallel to the leaf veins. Although they do not cause much damage, you should routinely check these areas since this is where you are likely to find the first eggs and larvae. Larvae can feed heavily on leaves, especially flag leaves, and can quickly cause significant yield reductions if they exceed the economic threshold of 25 eggs/young larvae per 100 tillers.

Winter Grain Mites

Wednesday, March 26th, 2008

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu and Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu

A number of fields were sprayed for winter grain mites in Virginia in late December and early January. In early February, a number of fields were also sprayed on the eastern shore of Maryland. Although we are now past the first generation, a second generation in March and April could cause additional damage. The following is an overview of this pest including pest identification, biology/life history and management options written by Dr. Ames Herbert from Virginia Tech.

“Winter grain mites attack small grains, including wheat, barley, and oats. Other hosts include grasses, especially bluegrass, bentgrass, ryegrass, and fescue. The mite also infests and damages legumes, vegetables, ornamental flowers, cotton, peanuts, and various weeds. Adult mites are about 1 mm long, black, with red legs and are fast moving. They quickly run to ground cover when you approach plants. As the name implies, they are winter pests. There are two generations per year. The first develops from over-summering eggs. Development begins after the onset of favorable temperature and moisture conditions in late September and October with populations peaking in December and January. The second generation develops from eggs laid by the first generation reaching maximum infestation density in March and April. Populations then decrease as temperatures exceed the range of tolerance. The females of this generation lay aestivating or over-summering eggs. (more…)