New Weed Management Website Launched

The new weed management website was unofficially launched this past week. You can visit the URL at http://weeds.cas.psu.edu/. The site is still incomplete and an evolving project. We hope to offer up to date information on weed management issues here at Penn State and also provide links to other useful sites. If you have suggestions for information or links you'd like to see, we'd appreciate the input.

Herbicide Performance and Rainfall
Well it is corn planting time and the forecast is looking dry. Dry weather can affect both soil applied and postemergence herbicide performance. All soil applied herbicides require rainfall to mobilize them for effective weed control. In general, rainfall should occur within 7-10 days after application or before weed emergence. As a general rule of thumb, 1/2 inch of rain is considered the minimum depending on current soooil moisture levels and the herbicide used. The less mobile materials (Prowl, Atrazine, etc.) and deeper germinating weeds (e.g. yellow nutsedge, cocklebur, velvetleaf, ragweed, etc.) will require even more rainfall for effective control.

Keep in mind that a number of residual herbicides can be applied after planting until corn and weeds reach a certain size or growth stage. The greatest risk of failure comes with trying to control annual grasses such as foxtail and panicum after they emerge.

However, several products are available to control emerged grasses (Accent, Basis, Basis Gold, Liberty on Liberty Link corn only, RoundUp Ultra and some other formulations of glyphosate on RoundUp Ready corn only, and Lightning on CL/IMI-corn only.) For most products, do not apply in liquid fertilizer if corn has emerged or injury may occur. Some delayed PRE or early-postemergence considerations are listed in Table 1.

If you have already applied a PRE and the 10 day limit has gone by following a soil applied treatment and weeds are starting to break, consider using a rotary hoe, making a post herbicide application, or start tuning up that old cultivator that you have been dying to try again.