Crop Scene Investigation - 18 Solved: What's been eating Bert's seedlings?

Monday, May 4, 2009

by CLARE KINLIN

What Bert initially thought might be frost damage turned out to be the work of wireworms. We found the long, cylindrical, copper-brown pest in the soil when digging up the damaged plants.  Wireworms are known to destroy germinating seeds and tiny seedlings, causing non-uniform growth or gaps in the stand. Plants appear wilted and leaves turn pale, sometimes becoming purplish-blue at the tips.

I explained to Bert that wireworms have a six-year life cycle, spending most of their life as larvae. In winter, they live in soil below the frost line and move to the surface to feed from April to June. Injury is more severe in wet, cool springs when the seed is slower to germinate. Due to their long life cycle, wireworms can damage several successive crops, feeding on the roots of weeds, grasses and crop plants.

In Bert's case, there was really nothing he could do to stop the feeding, apart from hoping for warmer weather. Wireworms migrate downward once soil temperatures increase, eliminating the threat to the crop. If conditions stay cool and moist, feeding continues and replanting may be necessary.

So what can Bert do to prevent wireworm damage next year? Scouting prior to planting is a wise decision. Know your risk by setting up bait stations to scout for wireworms approximately two to three weeks before planting.

Although seed treatments are not foolproof, they are a must. In this case, Bert used treated seed, but the pest was opportunistic by attacking the seedling, a stage when seed treatments offer less protection.

Early-season weed control would have also worked to Bert's advantage. Wireworms are most prevalent in fields with heavy grass infestations. It is likely the pests were feeding on the grass roots and, once Bert sprayed the weeds, the wireworms turned to attack the corn seedling roots.

While it's not always possible, planting into warmer soil conditions allows faster seed germination and seedling growth. This rapid plant growth helps avoid wireworm damage and preserve yields. Congratulations to Roy Nahuis, Wyevale for his correct answer. BF
 
Clare Kinlin, CCA, is a Sales and Agronomy Manager for NK® Brand, Syngenta Seeds, based near Prescott.