Potential Crop Pests In 2001

The best way to control any pest is to minimize the probability of it becoming a problem

By Dr. Michael D. Peel,
NDSU Small Grains Extension Agronomist
mpeel@ndsuext. nodak.edu

No matter how much change occurs in agriculture, crop pests will be a constant.  There is always a group of weed, disease, and insect pests that seem to reoccur each year.  Below are a few of my least favorite pests to monitor, and least-cost management strategies.

On the weed front, foxtails (green and yellow), wild oat, and kochia are consistent problems. Foxtails are most competitive when small grains are seeded late, and when soil temperatures are warm, favoring foxtail germination and rapid growth. Fields regularly chisel plowed generally have more foxtail than moldboard plowed fields. Moldboard plowing buries the foxtail seed, which prevents emergence and reduces viable seed for subsequent years.

Making a decision on whether to control foxtail in small grains is not always easy. Light foxtail infestations often will not decrease wheat and barley yields, but can cause harvest problems and result in heavy dockage.  Once a small grain is in the three to four-leaf stage, it can usually out-compete foxtail and make a herbicide treatment unnecessary.  However, if the foxtail population is heavy (100 plants/sq ft or more) control is generally needed. Foxtail emerging at the same time or before small grain is more competitive.

Wild oat, the undisputed scourge of small grains, is a cool season plant and germinates in the spring and fall when favorable temperature and moisture conditions exist. Cultural approaches to control wild oat in small grains include delayed small grain seeding, post seeding cultivation and competitive crops. Delayed seeding involves early soil cultivation to stimulate wild oat germination with one or two subsequent cultivations to control emerged wild oat prior to crop seeding. Besides the obvious extra cost of cultivation, delayed seeding of small grains past mid-May can result in yield reductions. Therefore, a combination of cultural and chemical control methods should be used to manage wild oat populations and prevent yield losses.

Good wild oat control with any herbicide requires proper timing of applications.  Early wild oat control can mean better yields because the weed has less time to compete with the crop. However, when a herbicide treatment is applied early, odds are that a late flush of wild oat will require a second application, or that some might escape. Any uncontrolled wild oats can reduce yields, and will produce seed that contribute to next year’s wild oat problem.

Kochia, the last weed I’ll mention, is exceptionally competitive, and just a few uncontrolled plants can cause severe yield losses. In general, the same cultural practices used to manage foxtail and wild oat will also help control kochia.  However, there are more herbicide options for kochia than the grasses. Herbicides that once controlled kochia such as the ALS herbicides may no longer be effective.  Choosing the herbicide combination that provides the best control is important.  The North Dakota Weed Control Guide is an excellent resource, one can be obtained by calling (701) 231-7881. You can also find information online at www.ext.nodak.edu/extpubs/weeds.htm.

Small Grain Diseases
Diseases that are most likely to be problems are seedling diseases, leaf disease, and of course scab (Fusarium head blight).  Selecting resistant varieties and using good rotations are the best management strategies for disease control.

Small grains are typically seeded into cold moist soils that inhibit growth of seedlings and favor growth of disease organisms resulting in seedling diseases.  Prolonged exposure to dry soils, which hinder germination, may also result in fungal decay. Shriveled, low test weight, diseased or weathered seed is more prone to attack by pathogens due to poor germination and reduced seedling vigor. Disease free seed and seed treatments can reduce the damage caused by decay, rot, and blight. Different seed treatments may be used depending on the purpose. Some treatments are a combination of fungicide and insecticide. Choose the treatment appropriate for the situation.

Scab development is favored by warm, humid, rainy weather during the period from flowering to maturity. Wheat and barley are affected by the scab in several ways. Floret sterility and kernel shriveling may lower yields and test weights, but more often the major concern is quality. Infected kernels can have the same size and shape as healthy kernels, making them difficult to remove with cleaning equipment. This increases the likelihood of a crop with high levels of DON that may result in market discounts.

The greatest risk of a scab infection is encountered when small grains are planted into last year’s scab-infected residue.  Hence, management for this pest starts before the crop is planted, by selecting the most tolerant varieties and rotation with a broadleaf crop.  Fungicides, such as Tilt and Folicur can reduce the severity of scab and control other leaf diseases.

Shriveled kernels and low yields are common symptoms when leaf diseases are prevalent. The causal agents for leaf diseases like tan spot in wheat and net blotch in barley survive in infected crop debris, grassy weeds, and sometimes in the seed. Outbreaks of these leaf diseases are usually accompanied by periods of high humidity or extensive dew.  Effective control of these leaf diseases is accomplished by rotation with broadleaf crops. Foliar-applied fungicides can also significantly reduce fungal leaf disease levels, and may prove economically beneficial when disease pressure and yield potential are high.

In the past couple of years, high levels of leaf rust have been observed on wheat in the region. Unlike other leaf diseases, rust cannot be controlled with rotations.  Rust spores overwinter in southern states and are carried north on the wind. Good varietal resistance is available for leaf rust and should be the main control strategy for this pest.

Good cultural control is one of many methods of controlling weeds and disease. Always plant weed and disease free seed, prevent weed seed proliferation, and clean tillage and harvest equipment between fields to minimize weed infestations.  The best way to control any pest is to minimize the probability of it becoming a problem.