Posts Tagged ‘black cutworm’

Agronomic Crop Insects

Thursday, April 1st, 2010

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

Alfalfa
Now that the weather has finally started to warm up, you should begin to sample for alfalfa weevil 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. In general, no treatment should be needed before you observe 50% of the tips with feeding damage. The most accurate way to time an application and try to avoid multiple insecticide applications 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. NOTE: The use of Furadan on alfalfa (as well as all other crops) has been cancelled and existing stocks CAN NOT be used.

Field Corn
In addition to black cutworm (which is generally a pest of later planted corn), we can also have a number of other cutworm species present in corn fields at planting time, including the dingy cutworm, claybacked cutworm and variegated cutworm. Information from the Midwest indicates that the claybacked cutworms can cause economic loss in corn. They overwinter as half-grown larvae in the soil so they can get a “jump” on black cutworms when it comes to cutting each spring. Since they are larger in size earlier in the spring, this species can damage very young corn plants. So, scouting fields at plant emergence is important, even if at-planting materials were used, to catch any potential problems. Just a reminder, if you plan to tank-mix an insecticide with an herbicide for black cutworm control, it should be done at, or immediately following planting.

During the winter meeting season, there was a lot of discussion regarding changes in refuge requirements for corn expressing Bt traits for the upcoming 2010 growing season. As of this date, the refuge in a bag strategy has not been approved for any transgenic corn product. However, there has been one significant change in refuge requirements for 2010 involving SmartStax hybrids. Because these hybrids contain 3 different genes for Lepidopteran control and 3 different genes for rootworm control, the EPA has approved a reduction of the standard 20% refuge to 5% refuge. In the last few weeks, I also received new information from Monsanto regarding placement of the refuge for SmartStax hybrids that applies to our area:

“The common refuge can be within or adjacent to the Genuity™ SmartStax™ field. If adjacent, it can be separated by a road, path, ditch , etc., but not by another field. Monsanto recommends planting the corn refuge for Genuity™SmartStax™ as an in-field or adjacent refuge as explained in this IRM/Grower Guide. However, if corn rootworms are not significant within a region, the common refuge may also be planted as a separate block that is within 1/2 mile of the Genuity™ SmartStax™field. This additional option to plant the refuge as a block within 1/2 mile is only available to farmers in the following States: AK, AL, AR, AZ, CA, CT, DE, FL, GA, HI, ID, LA, MA, MD, ME, MS, MT, NC, NH, NJ, NM, NV, NY, OR, PA, RI, TN, SC, UT, VA, VT, WA, WV, WY.”  Monsanto’s 2010/IRM Insect Resistance Management Grower Guide will be posted to their webpage in the near future. Also, be sure to contact your seed dealers for a full description of refuge requirements for 2010 for all hybrids that you plan to plant.

Timothy
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 necessary. If rust mites become a problem, Sevin XLR Plus (which had a 24(c) label on timothy for cereal rust mite management) now has a full section 3 federal label which includes pastures and grasses grown for hay and seed. The following is a link to the new label: http://www.cdms.net/LDat/ld332012.pdf. Be sure to read the label since there is new information on the number of applications per season as well as the days to harvest. For effective rust mite control with Sevin, the use of the higher labeled rate and at least 25 gal/acre of carrier to get good coverage of leaf surfaces generally results in better control.

Wheat
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 the presence of egg masses. The threshold for cereal leaf beetle has been adjusted to include sampling for eggs, especially in high management wheat fields or areas where problems were experienced the previous year. The eggs are elliptical, about 1/32 inch long, orange to yellow in color when first laid, changing to a burnt orange prior to hatching. Check our website for pictures of cereal leaf beetle adults, larvae and eggs: http://www.udel.edu/IPM/facts/clbpictures.htm.

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 1/4 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).

Agronomic Crop Insects

Friday, April 11th, 2008

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

Alfalfa
If you have not started to sample for alfalfa weevil, be sure to begin sampling fields 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. In general, no treatment should be needed before you observe 50 percent of the tips with feeding damage. A more accurate way to time an application and try to avoid multiple insecticide applications would be to sample stems and determine the number of weevils per stem. A minimum of 30 stems should be collected per field, placed top first in a bucket to dislodge larvae from the tips and 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, Mustang MAX, permethrin, Proaxis and Warrior. Furadan, Imidan, Lorsban, Lannate and Steward are also labeled for alfalfa weevil control.

Field Corn
In general, black cutworm trap catches remain low. However, we have started to see an increase in catches this past week. Although no precise numbers are available, moth catches of 9 to 15 moths per 7-day period have been associated with a moderate to high potential for black cutworm outbreaks in field corn. Larvae should be large enough to begin cutting when about 300 base-50 degree-days have accumulated since peak moth activity and egg laying. Pheromone trap catches can help determine when peak moth flight and egg laying occurs; however, they cannot predict the amount or magnitude of cutting that will occur.

We can also have a number of other cutworm species present in corn fields at planting time including the dingy cutworm, claybacked cutworm and variegated cutworm. Reports from consultants indicate that they have found higher numbers of cutworms while doing soil sampling for grubs earlier this spring. Information from the Midwest indicates that the claybacked cutworms can cause economic loss in corn. They overwinter as half-grown larvae in the soil so they can get a “jump” on black cutworms when it comes to cutting each spring. Since they are larger in size earlier in the spring, this species can damage very young corn plants. So, scouting fields at plant emergence is important, even if at planting materials were used, to catch any potential problems.

Just a reminder, if you plan to tank-mix an insecticide with an herbicide for black cutworm control, it should be done at, or immediately following planting. Insecticides combined with early burn-down applications, 2-3 weeks before planting, have not provided effective control. For the most recent pheromone trap catches, be sure to check trap catches posted weekly on the University of Delaware IPM website at (http://ag.udel.edu/extension/IPM/traps/currentbcwtraps.html)

Timothy
Be sure to sample fields for cereal rust mite activity. As soon as fields green up, you should begin checking for cereal rust mites and the early signs of infested leaves, especially in fields with problems in past years. These mites are microscopic, so the use of a 20x-magnifying lens is necessary. If rust mites become a problem, Sevin XLR Plus still has a 24(c) label on timothy for rust mite management. The following is a link to the 24(c) label for Delaware. (http://www.cdms.net/ldat/ld332028.pdf). You must have this label in your possession at the time of application.

Wheat
In addition to sampling for aphids, be sure to begin sampling fields for cereal leaf beetle activity. We can find evidence of adult feeding, so fields should be scouted early for the presence of egg masses. In recent years, the threshold for cereal leaf beetle has been adjusted to include sampling for eggs, especially in high management wheat fields or areas where problems were experienced the previous year. The eggs are elliptical, about 1/32 inch long, orange to yellow in color when first laid, changing to a burnt orange prior to hatching. Check our website for pictures of cereal leaf beetle adults, larvae and eggs: http://www.udel.edu/IPM/facts/clbpictures.htm

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 1/4 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).

Field Corn Soil Insect Management

Friday, March 28th, 2008

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

The following is a brief review of conditions favoring soil insects in field corn as well as observations from past seasons:

Corn Rootworm (Larval Control)
In general, rootworms continue to be more of a problem in continuous corn. Although generally more of a problem in heavier soils, we have also seen problems in continuous, irrigated corn fields planted in sandy soils. In our area, rotating out of corn is still a viable option for corn rootworm management. However, if you plan to plant continuous corn, control options include either a soil insecticide, a high rate of a commercially applied seed treatment, or a transgenic corn hybrid with resistance to rootworm larvae.

As far as seed treatments, reports from the Mid-West and areas in PA with heavy rootworm pressure state that “when rootworm densities and root injury have been low to moderate, seed treatments have provided acceptable protection of the roots. However, when rootworm densities have been high and root injury has been moderately high to severe, insecticidal seed treatments have not provided consistently acceptable control of corn rootworm larvae.”

Wireworms
High soil organic matter, sod covers, and heavy grass weed pressure the previous season all favor wireworm populations. In addition, damage from this insect is also higher in continuous corn. Commercially applied seed treatments i.e. Cruiser (thiamethoxam) and Poncho (clothianidin) have generally provided good wireworm control. NOTE – Labels for Cruiser and Poncho state seed and seedling protection.

Grubs
In general, grubs are favored by a number of factors including planting into soybean stubble, old sod, hay, pasture, or set-aside acreage. Cruiser and Poncho are labeled against white grubs. Although these 2 chemicals can work against low to moderate grub populations, in the past few years we have seen poor control with both products in commercial fields under high pressure, especially when the predominant grub species has been Asiatic garden beetle. If populations are high, you may still need to consider an in-furrow application of an insecticide. NOTE – Labels for Cruiser and Poncho state seed and seedling protection.

Black Cutworm
This insect is favored by late planting, broadleaf weed growth (especially chickweed) present before planting, poorly drained field conditions and reduced tillage. Rescue treatments can be applied for this soil insect if you are able to scout fields twice a week once leaf feeding is detected. Pheromone traps placed in the field by mid-March can be used to determine when to look for cut plants. So far, we have not caught any black cutworms in our pheromone traps. Look for pheromone trap counts in future reports. If you are unable to scout and you have conditions favoring cutworms, one of the following preventive approaches can be considered: (1) a granular soil insecticide labeled for cutworm control applied as a t-band, or (2) a tank mix of an insecticide with a pre-emergence herbicide or (3) a Herculex corn hybrid. In general, the seed applied treatments (Cruiser and Poncho) have not provided effective cutworm control in our area, especially if economic levels of larger larvae are present at planting.