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June 2, 2010

Some observations on small grains:

-With the wet weather we’ve been having I’m seeing more tan spot in wheat and some net blotch in barley.  These diseases can be effectively managed with fungicides.  During wet springs like the one we’ve been having, a fungicide application typically brings extra return on yield above the cost of the fungicide.    

-I’ve seen an article and had a question about early season insecticides in wheat.  The general statement is, “It doesn’t cost much so why not just throw it in the tank mix, just in case.”  In general, I would not recommend early season insecticides for small grains unless a specific field has a pest population above threshold.  The insect pest populations during this time of the season are typically low, well below any economic levels of injury.  The number one insect I’ve seen in wheat fields this time of year has been lady beetles, a beneficial insect that helps to control aphid populations.  Early insecticide applications can actually do more harm than good by killing these beneficial insects.  If a producer wants to enhance their tank mix and get more for their money, they would generally be better off increasing their fungicide rate rather than adding an unnecessary insecticide to the tank mix. 

-In addition to winter wheat and spring wheat volunteers, I’ve seen symptoms of wheat streak mosaic virus on barley, rye, and spelt. 

Clover Leaf Weevil: The Lesser of Two Weevils

A couple of county extension agents have asked questions about the clover leaf weevil.  Clover leaf weevils feed earlier in the season because they overwinter as larvae.  Alfalfa weevils, on the other hand, typically overwinter as adults and lay eggs during the spring.  Clover leaf weevils feed on the lower portions of the plant, mainly at night, and alfalfa weevils generally feed on the top portion of alfalfa plants.  The two species can be differentiated by size (adult clover leaf weevils are about twice as big as alfalfa weevils) and larval coloration.  Clover leaf weevil larvae have tan head capsules with a pink border along the white stripe on their backs (especially in older larvae).  Alfalfa weevil larvae have a dark brown to black head capsule without the pink border next to the white stripe.  Pictures of these pests can be found at http://ipm.illinois.edu/bulletin/pastpest/articles/200303e.html.   It is important to be able to differentiate between these two weevils because unlike their counterparts, clover leaf weevils typically do not cause economic damage in alfalfa. 

Additional sources: http://www.mda.state.mn.us/en/plants/pestmanagement/plant-pest-survey-program/pestfactsheets/alfalfa-weevil.aspx  http://ipm.illinois.edu/fieldcrops/insects/clover_leaf_weevil/index.html

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