Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Alfalfa
With the increase in temperatures, we are starting 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. 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
We continue to see a significant increase in black cutworm trap catches, especially in the Delmar, Laurel, Leipsic, Lincoln, Little Creek and Selbyville areas (http://ag.udel.edu/extension/IPM/traps/currentbcwtraps.html). We have also heard reports of cutworms damaging very early emerging corn in Maryland. In most cases, this damage was probably caused by the clay backed cutworm. As indicated in an earlier newsletter, they overwinter as half-grown larvae in the soil so they can get a “jump” on black cutworms. It is important to scout fields at plant emergence, even if at planting materials were used, in order to catch any potential problems. As a general guideline, a treatment is recommended if you find 10% leaf feeding or 3% cut plants.
Small Grains
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. In areas of the state where cereal leaf beetle have historically been heavy, we have seen a significant increase in egg laying activity and the first small larvae can be found. Be sure to check those areas carefully since damage can occur quickly if temperatures remain warm. The treatment threshold is 25 eggs and/or small larvae total per 100 tillers. This threshold is based on the number of eggs and small larvae present, rather than large larvae.
We continue to find low levels of sawfly and armyworms in small grains in Kent and Sussex counties. Once grain heads have emerged, you should begin sampling small grains for 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. 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.