David Owens, Extension Entomologist, owensd@udel.edu
Spider Mite Alert
New this year for us is participation in Syngenta’s Pest Patrol (https://www.syngenta-us.com/pest-patrol) a text to voice mail service that alerts subscribers when a new message has been posted that they can listen to on their phone. Subscribing is free, and the only time you are alerted is when a new post has been made available on crops that you select.
This week we have had several calls and field visits regarding spider mites. Recent rains have rejuvenated some of the weeds that spider mites are feeding on, but beware another stretch of hot dry weather. Under hot dry weather, mite populations can increase 10x per week. If you are not using any sort of magnification, it can be almost impossible to see the eggs and early instar spider mites under leaves. I like to use headband magnifiers such as Donegan’s OptiVisor. Although it only gives up to 3.5x magnification, it has a nice field of view and depth of field. While looking for stippling can be helpful, and often an indication of an infestation, sometimes older leaves do not reveal stippling until large mite populations are present. If you see stippling on younger leaves, check the undersides of older leaves carefully.
In soybean, sample mid to upper canopy leaflets. If stippling is present on more than 1/3 of leaves on approximately 10% of the plants sampled and there are nearing 20 mites per leaflet, a treatment should be considered. Last year, the best treatments were Agri-Mek SC and Zeal SC (note: these are the only labeled formulations for soybean) at mid-label rates. Lorsban and Dimethoate suppressed mite populations for about 2 weeks, Bifenthrin about 1 week. A single application of any of these three products should not be counted on alone to control mites.
Soybean
This week, we have started seeing Japanese beetle and green cloverworm in fields. Dectes stem borer will soon be emerging. As a general reminder, defoliation thresholds in full season bean fields prior to flowering are very conservative, and are also very high. It is also very easy to overestimate defoliation, especially from Japanese beetle, which skeletonizes upper leaves. When evaluating defoliation, look at the entire canopy.