Weeds are not only a nuisance, but also can be a resting home for insects and diseases, which can wreak havoc on production crops such as tomatoes. With this in mind, growers need an effective weed management plan so they can raise weed-free tomatoes and ensure they won’t experience a reduction in yield and quality.
Planning a strategy
To develop an effective weed management plan, first identify the weeds present. Extension agronomist Stanley Culpepper indicated in the University of Georgia Commercial Tomato Production Handbook that one of the best ways to identify weeds is by weed mapping, which consists of surveying each field in the fall and recording what weed species are present as well as numbers present.
Culpepper said weeds that growers can expect in their fields are summer annuals, including yellow and purple nutsedge, morning glory, purslane species, nightshade, pigweed and annual grasses.
In “Commercial Production of Staked Tomatoes in the Southeast,” plant pathologist Kelly Ivors with North Carolina State University said a good weed management program involves inspecting each field because every field has its own weed species, fertility issues, soils, and yield and quality potential. She advises growers to scout fields one or two times per week, use herbicides if necessary and consider hand removing weeds less than 3 inches tall if chemicals don’t work. She added that studies have shown that one to three Palmer amaranth plants per tomato hole can harm yield by 67 percent and reduce the amount of tomatoes by 61 percent.
A second point in good weed management is to see that growers raise a healthy plant. That means it should be free of weeds, insects and diseases. The establishment of a large plant canopy will assist in reducing weed growth.
In addition to a healthy growing tomato plant, one free of insects and diseases, Culpepper stresses part of a good weed management plan consists of following cultural practices such as ridding seeds and transplants of weeds, preparing an effective seedbed, fertilizing and watering when needed, establishing row spacing, selecting the best site for planting (one preferably with little weed and disease pressure), creating a crop rotation plan that works well with tomatoes and cleaning equipment and workers’ shoes when going from field to field so they stop the spread of new weed species.
Additionally, Culpepper suggests growers either plow, disk, cultivate or till, mow, hoe or pull weeds by hand if necessary to rid fields of them. Use of mulch may limit some of these practices, but is a practice that may increase plant yield and help reduce weeds for a healthy plant. If left unchecked, weeds can reduce yield by 50 percent, even if growers raise their tomatoes under plasticulture, he said.
A word of caution, he noted, is that nutsedge will come through mulch, and some weeds tend to peek out of the transplant hole. In this case, he advised growers to fumigate or apply herbicides when using mulch. If alternatives are available, he advised using them since growers can no longer apply methyl bromide.
Ivors noted that nutsedge will particularly be troublesome in a plasticulture environment since methyl bromide has been phased out.
As part of their weed management plan, growers have identified the weed species present in their fields. Next, they must figure out how those herbicides affect tomatoes and how they should apply them, Culpepper advised. They also should consider postemergence herbicides, monitoring fields closely even after they have applied them so they can determine if the herbicide has been effective. He warned growers to be careful when applying herbicides atop mulch before planting. They can remain in the mulch and damage tomatoes that are planted later.
Ivors further cautioned that after a rain or irrigating, herbicide residue can slip into the tomato hole. She indicated the result can be a damaged or even dead plant. Before transplanting in the plastic mulch, she advised washing off herbicide residue with water.
When applying herbicides, Ivors reminded growers to apply lower rates on sandy soils or those with low organic matter. Those with clay soils or soils with a higher organic content should use a higher rate. Also, she stressed that not all herbicides will control all weeds. That is why it is so important to identify the weed species present and select the right herbicide for the weeds in each field. She suggests referring to the “Southeastern Vegetable Crop Handbook” for more details.
Research and ask before applying
Before using any fumigant or herbicide they are unfamiliar with, growers should consult with their local Extension agent or specialist and read and follow the herbicide label carefully.
Remember, weeds compete for the light, water and nutrients of tomato plants. To stop them in their tracks, develop an effective weed management plan and refer to it often. In addition, fields free of weeds help reduce insect and disease infestation. Eliminating or reducing them is a win-win for healthy, juicy and large red tomatoes.