By: Allen Knutson, Kevin Ong, James Kamas, Bill Ree and Dale Mott
Insects and diseases can cause problems in peaches, plums, nectarines and pecans. Homeowners who grow these fruit trees can more easily identify the problems and select the proper control methods if they are familiar with insect pests and diseases, their life cycles and the damage they cause.
Because such problems vary from one area of Texas to another and from one year to the next, it is important that you keep records of pest and disease occurrences. These records can help you make wise control decisions, such as on the timing of pesticide applications.
Plant diseases are most severe in periods of frequent rain or dew and mild temperatures (75 to 85 degrees F). Early-maturing peach varieties are more likely to be affected by brown rot than are late-maturing varieties; late varieties are often damaged more by peach scab.
Insect infestations are not as dependent on weather as are diseases. Most insect pests are monitored by visually inspecting trees for insects or their damage. Traps baited with pheromones can be used to monitor activity of the pecan nut casebearer and the lesser peach tree borer.
Healthy plants can survive some insect and disease damage better than can stressed plants. Trees grow best if you select adapted disease-resistant varieties, plant them in a suitable site, follow a well-balanced fertility program, and irrigate and prune as needed.
It’s important to clean up and dispose of plant residue to reduce the damage from peach scab, plum curculio, hickory shuckworm, and brown rot of peach. Diseased material that is properly composted can be recycled as mulch or organic material.
Homeowners face a number of problems in buying chemical products to control diseases and insects. Some products have had their uses canceled or are not as available to homeowners as they once were, and the most effective ones are not always packaged in small quantities and may only be available in commercial-size packages.
If you buy commercial-size packages, the cost is high, the unused portion must be stored for a long time, and the label lists the rates in amounts per acre, which is difficult to convert when mixing a few gallons of spray material.
Another problem is that many products have limits on the number of times they can be applied per season. These limitations may require that you buy more than one chemical to achieve season-long control of diseases or insects.
In some cases, a commercial-size package is your only option. The number of larger packages was limited as much as possible in this guide, but that also limits the pesticide selection. To get a bigger selection, fruit hobbyists with more than a few trees should consider commercial-size packages. For homeowners with just a few trees, the best option may be the combination (insecticide plus fungicide) products available at nursery and garden centers (see Table 6).
Pesticide products available in small packages are listed in Tables 2, 4, 5 and 6. However, this list may not be complete.When buying a pesticide, be certain that you will be using it for the purpose stated on the label.
The spray guide for pecans is based primarily on insect biology and life cycles, because, generally, more pecan losses are from insects than disease. If you plant scab-disease-resistant varieties, you may need to treat only for insects. Another reason to concentrate on insect control is the fact that pecan fungicides are available only in commercial-size packages. Apply zinc foliar sprays frequently at the beginning of the season.
Large pecan trees are difficult to cover thoroughly with pesticide sprays. Hose-on sprayers can be used to spray trees 25-30 feet tall. When larger trees must be sprayed, employ a certified commercial pesticide applicator.
Peaches and plums
The most important times to apply disease and insect control products are at petal fall, shuck split and preharvest. You can use combination products (insecticide and fungicide together) for early- and mid-season treatments, but most of them have harvest limitations that prevent application close to harvest, when brown rot control is critical.
Fire ant management
Fire ants can be a severe problem with pecan and small fruit production both in agriculture and in urban areas. These ants can damage equipment such as electric motors and irrigation systems; their bites can interfere with harvest and cause medical problems.
Several insecticides are available for producers to use to manage fire ants. With the many possible application sites in an urban area, it is up to the individual to read the product labels for information on where they can be applied and at what rates.
When using baits either for individual mound treatment or as a broadcast application, follow these recommendations to improve bait effectiveness:
- Always use fresh bait. Avoid packages that have a rancid odor. Baits with a strong rancid odor are probably spoiled, and the ants will not be attracted to the bait.
- Store unused bait in cool dry place in a sealed container.
- Avoid applying baits if rain is expected in 12 hours.
- Before baiting a large area, conduct a prebait test by placing a small amount of bait in an area near mounds. Check the baited area after 1 hour to see if ants are gathering the bait. If they are not, conduct another prebait test in a few days.
For additional information on fire ants, see Texas Cooperative Extension publication B-6043, Managing Imported Fire Ants in Urban Areas or visit the Texas A&M fire ant web site at http://fireant.tamu.edu.
Before using any pesticide, carefully read all the instructions on the container. Follow instructions such as for wearing protective clothing during mixing or spraying. Take the necessary precautions when applying pesticides to avoid being exposed to chemicals.
Mix pesticides in a well-ventilated area or outdoors. Avoid chemical contact with your skin, and do not breathe chemical vapors.
Apply the pesticides at the proper rate. If you use less chemical than is prescribed, it may not control the pests well; if you use more than is recommended, you may damage the plant or leave too much residue on the fruit.
Store chemicals in a secure area away from pets and children. Prepare only the amount required for one application. Dispose of any unused, diluted sprays and empty pesticide containers properly. Store pesticides in their original containers.
The pesticides suggested in this guide are registered and labeled for use by the Environmental Protection Agency and the Texas Department of Agriculture. Regulations on pesticides are subject to change and may have changed since this publication was printed. The USER is always responsible for the effects of pesticide residues on livestock and crops, as well as for problems caused when a pesticide drifts or moves to others’ property. Always read and carefully follow the instructions on the container label.
For more information, contact your county Extension agent.
Organic pest management
Some fungicides and insecticides are made of naturally occurring ingredients and are considered acceptable for organic gardening. For allowed products, refer to the Texas Department of Agriculture Organic Certification Program Materials List (TDA publication Q694A).
Peaches, plums, nectarines and apricots: Use sulfur fungicides throughout the spray program. Make applications at the shortest interval allowed. Shortened intervals are important during the late-bloom, shuck-split and first-cover periods and again during the preharvest period. These are periods when fruit diseases are the most damaging.
Pecans: Copper sulfate is considered an organic fungicide, and some formulations are approved for use on pecans to control pecan scab and other foliage diseases. Copper sulfate is highly toxic to fruit trees such as peaches, plums, apricots and nectarines and to some ornamental plants. Be careful when using this product near sensitive plants if there is a possibility of drift.
General considerations: For infection to occur, most plant diseases require that the leaf, fruit or nut remain wet for a certain period. The following precautions reduce the length of time the plant is wet after dew or rainfall:
- Prune the trees to allow sunlight to penetrate the leaf canopy.
- Space the trees to allow for air circulation.
- Plant the trees in an area that will receive early-morning sun and where air circulation is not blocked by buildings or other plants.
- Avoid wetting trees during irrigation.
Select varieties that are naturally resistant to the major diseases of your area. Resistance does not mean that the plants are immune to infections. Fungicide applications are usually more effective on plants with some resistance.
Download a printer-friendly version of this publication: Homeowner’s Guide to Pests of Peaches, Plums and Pecans
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