The list of herbicides registered for melons is limited although most of the grasses can be controlled with the available products. Prefar, Dacthal and Tifluralin are registered preemergence but only Prefar can be put on before the crop has 3 leaves. Up to 9 qts. of Prefar can be but on preemergence either before or after planting. Prefar does not incorporate well with drip or furrow irrigation. It works best when incorporated with high volumes of overhead sprinkler water. Mechanical incorporation also does not work well. Dacthal and Trifluralin can only be used as layby treatments after the melons have 3 or 4 leaves. Both of these herbicides can cause unacceptable injury if applied too early. Many grasses will have emerged by this time and will not be controlled with any of the preemergence herbicides. They must be removed mechanically, by hand or with one of the postemergence grass herbicides.

The postemergence selective grass herbicides were developed almost 30 years ago. These include fluazifop(Fusilade-1985), sethoxydim(Poast-1986,Segment,Vantage and others) and clethodim(Select-1991,Select Max, Arrow, Envoy, Volunteer and others). They only control grasses and are registered on melons and many other broadleaf crops as well as trees and vines. They can be slow acting, especially during the cool months and have no soil activity. Because of the continual emergence of many grass species, it is not uncommon to have to make more than one application to achieve season long control. They are all fairly broad spectrum and will control most grasses although only clethodim will control sprangletop and annual bluegrass and these must be small. None of them will control sandbur.

Cartoon: Barry

To contact Barry Tickes go to: btickes@ag.arizona.edu.

For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.