Western / Northern Corn Rootworm by Danielle Stannard

With the increase in Non – GMO corn across New York State this season, we’ve been seeing an increase in pests, as well. If you’ve seen the insect pictured above in your crop fields – you’ve seen the Western Corn Rootworm (Northern Corn Rootworm pictured below).

 

Western Corn Rootworm

• Scientific name: Diabrotica virgifera virgifera
• ¼ inch long
• Yellow with black stripes on the wings

 

Northern Corn Rootworm

• Scientific name: Diabrotica barberi
• ¼ inch long
• Yellow to pale green beetles

 

What Kind of Damage Do They Do?

 

The larvae affect the roots of corn from early June to late July. However, you can find the WCR or NCR adults in corn silks, tassels, or foliage until late September. The most severe damage that rootworm causes is lodging because of root pruning. Pruning the roots reduces the nutrient and water uptake which causes stress on the corn. The adults    clip the silks during pollination which in return interferes with pollination of the plants especially under stress. NCR are also found to be feeding on pollen nearby whereas WCR beetles are known to feed on the leaf surface.

 

How Do You Scout For Rootworm?

 

When visiting your fields if there is rootworm in the cornfield one year, chances are it is an indicator that next year that field will suffer from the same problems. The only way to predict the potential damage is to count the WCR and NCR adults from mid-July to early September.

 

It is important to scout the fields that will potentially be corn the following year weekly to get an accurate count. When counting you should examine 2 plants randomly in each of the 25 areas of the field, counting the number on each plant. While scouting, approach the plant calmly to avoid allowing the beetles to get away before you get an accurate count, also making sure you count the plant in its entirety.

 

Once you have recorded your numbers, if the average per plant is more than 0.75 adults in corn after corn or 0.5 adults in the first-year corn, plan to rotate to another crop in that field or apply an insecticide the following season. Another management control could be applying an insecticide to prevent them from laying eggs and over wintering.