Weather Causes Weed Challenges

Cool, wet conditions have resulted in weed management challenges for most producers. The first challenge has been getting on the field to spray. Delays have resulted in producers spraying in less than optimum weather conditions and / or crop / weed growth stage conditions, resulting in less than adequate weed control and crop phytotoxicity which results in subsequent yield loss. We have also seen a lot of herbicide drift onto sensitive horticulture crops.

The second challenge has been common weeds emerging later than normal, which again causes difficulties with spray timing (ie. the crop is passed the safe stage for application).

The third challenge has been higher densities of weeds that perform well in cool / wet conditions; such as, barnyard grass and chickweed.

The fourth challenge has been slower burn down or visual weed control, which leads producers to believe that their herbicide has not worked. Typically, the herbicide is working just slower than normal. This issue tends to result in an increased number of herbicide applications, causing the potential for more resistance management issues in the future if products are not rotated.

Remember, weeds are extremely adaptive and prolific. You will never have exactly the same weed problems in your fields each year. In cool, wet conditions plant metabolism slows, until conditions improve making herbicide uptake and coverage difficult.

If we were having a hot, dry year the problems would be different. In drought conditions weeds grow thicker cuticles which serve as a barrier to herbicide absorption and harden off with thick stems and deep root systems competing with the crops for moisture. And in extreme heat plant leaves roll up to minimize moisture loss, again making herbicide coverage and uptake difficult.

Timely weed control is even more important when crops are stressed because the weeds are competing for limited resources - nutrients in wet solids and water in drought conditions.

The best thing producers can do is monitor the growth stages of both their weeds and their crop, apply herbicides when the weeds are actively growing and small to ensure good control when weather conditions are less than optimal.