What are tips for using preemergent herbicide on citrus?

By Chris Boisseranc
Southwest Ag Consulting Inc., Redlands

A decade ago, growers relied on postemergent sprays because the cost of Roundup was so affordable. During the past five years, many growers have moved to a preemergent program.

Preemergent herbicide sprays are critical for maintaining weed management throughout the season. There are many glyphosate-resistant weeds, including hairy fleabane, horseweed and other grasses. A preemergent application prior to germination or very soon after is essential to managing these weeds.

Several preemergent chemicals work well on resistant weeds. Application timings usually occur during the winter, so there is rainfall to push the preemergent into the soil.

A broadcast application with a boom sprayer is commonly used for making an application. It is sprayed across the grove, putting a sealant on the entire orchard floor. It is important to have weed control already in place so there is good contact with the orchard floor.

Timing is critical when making a preemergent application. A quarter to a half an inch of rainfall is needed about a month after the application. 

Drought years are more difficult because most citrus groves are on drip irrigation, so water can’t get to the middle of the orchard. While the middle of the rows can’t be treated effectively, the sprinkler lines can be, and there is often significant germination. Some preemergents can be applied through chemigation. In these situations, the middle of the rows would be mowed.

With preemergents, growers see better control of noxious weeds, and they can be cost-effective, too. One application can do what would take several postemergent applications, and preemergents can provide at least four to six months of control. 

January to February is good timing for a preemergent application on navels and tangerines. A grower can harvest and prune, then follow with a preemergent application and set the grove up for weed control for the next several months.