We’ve all heard before how weeds can damage crops such as spinach, carrots, cabbage, but seldom do we hear the potential losses associated with weed infestation.

Well, Texas A&M folks have mentioned just a few losses in the Texas Vegetable Growers Handbook that growers might find interesting. Lynn Brandenberger, formerly a horticulturalist at Texas A&M and now a horticulturalist and professor in the Vegetable Department of Horticulture & Landscape Architecture at Oklahoma State University; and Frank Dainello, an emeritus horticulturist formerly at Texas A&M, noted that growers will see yields reduced because weeds compete with plants, in this case, spinach plants.

In addition, these same weeds can block light, nutrients and water from entering the plant, thus possibly reducing yields, they noted. Also, growers may have to pick and choose crops they plant due to a possible heavy weed infestation. Another occurrence in losses is when so many weeds grow, especially during harvest time. Too many weeds can make harvesting more difficult, may increase labor necessary to pick the vegetables or fruit, and it may even prohibit growers from using mechanical harvesters. All this can drive up the cost of spinach and other crops at the store or roadside markets. In trying to control weeds when crops mature, growers may damage roots, leaves and or stems when they try to cultivate. Additionally, repeated cultivations to control persistent weeds may damage the soil structure like when too wet. This could harden the soil or produce clods if the land is a heavy clay type. Those clods are difficult to break up and can prevent growers from shoving dirt to the plants.

More losses can occur when weeds shelter insects and promote disease, according to Brandenberger and Dainello. A bunch-type plant like spinach can easily harbor a number of insects and diseases. Aphids and maggots can live within wild mustards and attack cabbage, cauliflower, radish and turnips. Virus diseases can affect watermelon, as another example.

Growers know that heavy weed infestation can reduce quality, leaving growers with less money for their products. Customers likely won’t buy them if they see a blemish on the produce, or if they see an odd-shaped product marketed at the farmers market or grocery store.

Weeds can even stop the flow of rainwater or irrigated water from reaching the plant, they noted. This redirected or stoppage of water can reduce efficiency of the water delivery system, which can starve the plant of necessary moisture and nutrients, and, in some cases involving drip irrigation, it can block the necessary liquid fertilizer from reaching the plant, thus preventing growth.

Weed management

So what’s a grower to do? He can either prevent weeds from growing in the first place, control them or simply eradicate them, according to Brandenberger and Dainello. A grower can prevent new and perennial weeds by stopping them from breaking through the soil. He also can avoid carrying them from field to field with machinery, his hands, shoes or water. He can prevent existing weeds from flowering, thus stopping them from seeding. Prevention is advised as the best way to stop weed growth.

Brandenberger and Dainello indicated that limiting weed infestations can actually control them because their numbers are smaller, providing less competition with the spinach plant. However, they stress that achieving control is a balancing act between labor costs that can increase or some herbicides that may cause damage to the crop.

A sure-fire way to control weeds is to kill or eradicate them from the field, they suggested. Elimination can mean destroying spinach or some other crop, or trying to eradicate the weed seeds, which is more difficult to do, they indicated. Cost involved to kill weeds may be prohibitive for the grower because it may take a lot of time and money to carry out this task.

Identification

Before growers can prevent, control or eradicate weeds, they are wise to identify or classify weeds in their fields. This identification involves determining how long a weed is likely to live, when a weed grows best and how a weed reproduces, according to Brandenberger and Dainello. Naturally, when it comes to weeds, you have summer and winter annuals, biennials and simple and creeping perennials. Annuals live one year. Biennials live more than one year, but not more than two years. Perennials live more than two years or sometimes indefinitely, they indicated.

Identifying weed species in a field is important, too. For a proper weed species identification in fields in a particular area of the country, it is best to contact your local Extension agent or specialist.

Herbicide types and application

Proper identification goes for proper herbicide control, too, but to help growers who may not be as familiar, there are three types of herbicides: contacts, growth regulators and soil sterilants, according to Brandenberger and Dainello. They pointed out that contact herbicides cause rapid drying of plant tissue. A paraquat would be a good example. Growth regulators control physiological plant processes such as cell division or expansion. They also may inhibit a plant from converting light into food energy. A good example is 2, 4-D. Soil sterilants are used to kill all plant growth. Persistent ones are used on noncropland such as railroads. Nonpersistent ones can dissipate from the soil, and those used in vegetable production, for example, include Vapam and methyl bromide, (the latter is being phased out by the Environmental Protection Agency).

Before applying, learn what a preplant treatment is. According to Brandenberger and Dainello, a preplant treatment is one that growers make before planting spinach. A preemergence herbicide is one applied prior to emergence of a crop or weed. A postemergence is an application that growers make after a crop or weed has emerged from the ground.

In conclusion, weeds can cause crop losses, quality wise and economically. Know what those possible losses are, identify the species of weeds in your fields and learn more about weed control for the most effective ways to prevent, control or eradicate them.