FEATURE | farm management

The Perfect Time for Controlling Weeds

The Right Steps in Summer Can Reduce Seed Bank

Summer is a great time to control the weeds that will be problematic during next year’s harvest. When the bushes begin to flower, the most prevalent weeds are cool-season annuals, but as the berries develop, the temperatures rise and warm-season weeds begin to emerge. These warm-season annuals will grow, develop seeds, and contribute to the seed bank. The summer months provide an opportunity to prevent this contribution to the seed bank.

Herbicide selection should focus on rotating modes of action or active ingredients that are not used during the fruit production. Some herbicides have a limited range of weed species that are controlled. This is an opportunity to include a.i.s that broaden the control. If a weed management program includes flumioxazin or indaziflam, then consider sulfentrazone, simazine, diuron, or other pre-emergence herbicides. The focus is on pre-emergence herbicides so that post-emergence herbicide applications are minimized and maximum amounts per year are not reached during the production times.

Non-chemical weed control measures should be included with herbicides. Mowing the weeds can prevent the weeds from producing flowers and seeds. If the plants already have seeds, then blow the clippings away from the crop row or remove them from the field. Hand weeding can be used for the most problematic weeds. 

Spanish needle is a warm season annual that can proliferate quickly in the summer. The herbicides may appear as inefficient, but it is a numbers game. Spanish needle can produce 1,500 seeds, an herbicide can provide 90% control, and 150 seeds will still emerge. Pre-emergence herbicides that work well are flumioxazin, indaziflam, and sulfentrazone. Post-emergence herbicides include glufosinate or diquat. Spanish needle has shown some tolerance to glyphosate in citrus and blueberry.

Yellow and purple nutsedge are perennial weeds that enjoy the hot and wet Florida summer. The best control options are herbicides that can translocate to the underground tubers. Apply glyphosate or halosulfuron to the heaviest infested areas of the field. Do not apply these products after pruning. The plants are moving water and nutrients to the cut ends of the plant, and the herbicide will also translocate causing significant injury.

The warm-season annuals will grow extremely fast during Florida’s heat, but control now is important for reducing the weed seed bank. Taking the time during the summer will reduce the weed management needs when fruit is on the bushes.

CREDIT:
Peter Dittmar, Associate Professor, Horticultural Sciences Dept.