PAINTED LADY BUTTERFLIES TAKING OVER - By Randy Pryor

   Large populations of painted lady butterflies have been reported in a number of locations across the state.  I call them miniature monarchs because of some similarities.  The main concern about these populations is whether these adult butterflies will lay eggs and the subsequent larvae (thistle caterpillars) will be a problem in soybean fields. Typically, painted lady butterflies fly northward during the summer, so butterfly numbers should decrease over time.

   We do not recommend that growers apply pesticides to control adult painted lady butterflies, however, they should scout their soybean fields for defoliation from thistle caterpillars and other insects. Treatments can be made in reproductive stage soybeans when defoliation exceeds 20%.

Proper estimation of the defoliation is essential for determining if an application is necessary.  Pictures are helpful.  To see those go to: http://cropwatch.unl.edu/2017/large-populations-painted-lady-butterflies

   Painted lady butterflies lay eggs singly on soybean plants with egg hatch occurring in about seven days.  After hatching, the larvae will feed for two to four weeks with 97% of their plant tissue consumption occurring during the last two larval instars.  During this time, the larvae are typically found in the upper canopy of a soybean plant and damaged plants are usually found at the field edge. The caterpillars also form webs by tying the leaves together, creating a protective area for them to feed.

   Painted lady or thistle caterpillars do not exclusively feed on soybeans and are found on over 100 species of plants including Canada thistle, sunflower, aster, ironweed, red clover, etc. After feeding, the larvae will pupate over a period of 7-17 days with two generations per year in our area.

   The temperatures with cool weather the past 10 days, may help the current situation. Bacterial and fungal pathogens of thistle caterpillars thrive under these types of environment. Insecticide applications may not be necessary if significant numbers of caterpillars are infected.

SCHEDULING LAST IRRIGATION ON CORN

   From beginning dent to black layer, field corn typically will use 5 inches of water to finish over a 24-day span in August.  A full profile down to 4 feet on a silty clay loam soil will typically hold at 50% field capacity 4 inches of available water.  For corn to mature is dependent on growing degree days. If corn needs 5 inches of water to reach maturity and we receive some hot windy days in late August, the corn will still use 5 inches, it will just finish up a few days quicker.  Take a look at our predicted late season water use on crops at: http://cropwatch.unl.edu/scheduling-last-irrigation-season

    UNL Extension has a free app for iPads and smart phones called CropWater that works great with watermark sensors.  It’s really handy to use on corn, soybeans, dry beans and sorghum.  You can select crop growth stage and 50 or 60% depletion this time of year and predict whether that last turn with the pivot is a waste of precious water and money.

   For example, if your readings are 30, 50, 3 and 3 or for each 12 inch depths and you select allowable soil water depletion at 60%, the app calculation says effective rain and/or irrigation only needs to be 0.78 inches.   As we near the end of the season, we can push the threshold to 60% depletion. This is the time of year where management information from the sensors shine.