One undisputable lesson learned thus far in the 2017 growing season is that weather can wreak havoc with the best-laid plans. Based on phone calls, grower conversations, and observations of our Wayne County Extension integrated pest management (IPM) scouts there are also a number of pest issue questions that need to be considered. In this column, I will summarize some of the early season pest conditions occurring in our area.
Slugs are not an insect, but rather a mollusk, and are in plentiful supply this season. Our wet weather has favored slugs thriving. Slugs feed on a variety of crops, damaging both agronomic and horticultural crops. Deciding whether to treat for slugs depends upon the stage of crop, the extent of the damage and economics. Treatment options are limited, either metaldehyde or iron phosphate bait products. Although there are no hard and fast economic thresholds, one guideline suggested in OSU Extension bulletin 545, “Control of Insect Pests of Field Crops” says treatment may be necessary if the new growth has greater than 40% defoliation or if more than 3% of the plants are killed by slug feeding. Uniform application of bait products is necessary to get good slug control. For the metaldehyde product, there should be 4-5 pieces of bait per square foot. Warm weather and favorable growing conditions often allow crops to grow fast enough to minimize slug feeding. Once corn reaches the V-6 stage of growth, a rescue treatment with a bait product is rarely justified.
Some areas of the county have reported heavy numbers of armyworms. The guideline for rescue treatment is if stand infestation is greater than 20% and less than 50%, consider rescue treatment when corn is at early-whorl stage, or larvae are less than 1 inch long, or more than one larvae per plant, or de-foliation of infested plants exceeds 50%. If stand infestation is greater than 50% and larvae are not mature, apply a rescue treatment immediately. Evaluate larvae size because larvae feed until they reach about one and a half inches in length before stopping their feeding to pupate.
Eastern flower thrips have damaged the strawberry crop for a number of area growers. Eastern flower thrips damage the flowers and developing fruit, which results in a bronzing of the fruit and hard, tough berries that do not mature normally. Unfortunately, once growers notice the symptoms it is too late to rescue the crop. Scout for thrips when berries begin to flower. If 2-10 thrips are found per blossom then a rescue treatment should be applied. If the berry crop is done flowering there is no economic reason to treat, even if thrips are present because thrips do not affect the health of the berry plants, they only damage the fruit. However, if growers also have raspberry plants, they should scout those plants at flowering because thrips could move into that crop.
One other insect pest that has shown up earlier than normal this year is potato leaf hoppers (PLH). Our IPM scouts are finding PLH in both horticultural crops and in alfalfa. Alfalfa growers should be sweeping their fields to determine PLH levels. Growers should sample 5-6 random areas for each 25 acres of alfalfa. A sample is defined as 10 sweeps of a sweep net. Apply a rescue treatment if the average number of PLH adults and nymphs in a 10-sweep sample is equal to or greater than the height of the alfalfa sampled. For example, if average of five sweep net samples is 12 PLH and the average height of the alfalfa stand is 12 inches or less, then apply a rescue treatment. If the stand has been planted to PLH resistant alfalfa, then the threshold is three times the normal economic threshold. Considering our previous example, it would require an average of 36 PLH per 10-sweep sample before triggering a rescue treatment.
As the average plant height increases, taking an early harvest rather than applying a chemical rescue treatment is another option.
Finally, anytime a pesticide is used, the grower should read the pesticide label and understand how to properly use the pesticide. The pesticide label is the law. The label contains important information including rate, mixing directions, personal protective equipment required during mixing and application, the pre-harvest interval, nozzle/droplet size, application pressure, environmental considerations and more.
Contact the Wayne County Extension office at 330-264-8722 for more information about crop pests and/or pesticide applications.