David Owens, Extension Entomologist, owensd@udel.edu
Seedcorn Maggot Active
We are approaching degree day targets for Seedcorn Maggot in Georgetown. Adult flies were observed Wednesday in Lewes. According to the forecast period, we are heading into a cooling trend, I do not know what that will mean for early flight pressure on peas but suspect it will not be as intense as previous years. That said, still make sure you have an insecticide seed treatment on peas!
Allium Leafminer
Allium leafminer is a pest of onion, green onions, shallots, leeks, and garlic and was spotted throughout the state last year causing damage to alliums. Penn State has a good fact sheet on it here: https://extension.psu.edu/time-to-prepare-for-protecting-allium-crops-from-allium-leafminer. In Georgetown we will be at or very close to the target degree day threshold of 350 Celsius degree days (base temp 1 C) at some point during the first week of March. You can use the NEWA weather tool to calculate degree days from the closest weather station to you: https://newa.cornell.edu/degree-day-calculator. Good control options include row covers for March and April and systemic insecticides used with a spreader type adjuvant. Scorpion, Exirel, Radiant, and Entrust (OMRI) are the most effective materials, are translaminar or systemic, and will have the longest residual activity. Repeat applications a couple of times during the adult flight period which typically lasts 5-6 weeks. Pyrethroids should be applied more frequently.
Tree Fruit
The window for controlling peach leaf curl diseases is closing. This disease can be easily treated with a fungicide application before buds begin to swell. Check out this UC fact sheet: https://ipm.ucanr.edu/PMG/PESTNOTES/pn7426.html.
Small Grains
Greenbug, while generally uncommon, may be overwintering in our area this year due to the mild winter. It is light green, has short, green cornicles or ‘tail pipes’ and often has a bluish streak down the back. It looks pretty similar to English grain aphids except EGA has longer, black tailpipes. Earlier this month we scouted 6 malting barley fields, average aphid counts ranged from 3 to 40 per square foot. Typical small grain thresholds are around 100 per ROW Foot. We are starting to see some parasitic wasp and syrphid fly adult activity in fields. Treatments for aphids are usually the most cost effective when applied in the fall and in fields with a history of barley yellow dwarf virus.
Slug Factsheet
A new fact sheet on slugs is available from University of Maryland: https://extension.umd.edu/resource/managing-slugs-field-crops-using-ipm-principles-fs-2022-0629.