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Osage Orange Control

Osage orange is a medium-sized tree with milky sap that will grow to 40 feet (12.2 meters) tall. Bark is light gray-brown tinged with orange. Bark on large trees separates into shaggy strips. Twigs are orange-brown with a zigzag shape and have sharp axillary spines on vigorous juvenile growth. These spines may be infrequent or absent on mature, slow-growing trees, but will return on sprouts from such trees. Leaves are alternate, entire, shiny, ovate or ovate-lanceolate, and long pointed at the tip.

Staminate and pistillate flowers are born on separate plants. Flowers are tiny. Staminate flowers form short clusters and pistillate flowers are crowded into spherical heads. The multiple fruit is large, spherical, and fleshy. The green-yellow fruit can be up to 6 inches (15.2 cm) in diameter and contains many seeds. These fruits are hazardous during abscission in late September to early November, and workers should wear hardhats around female trees. Osage orange should be accurately identified before attempting any control measures. If identification of the species is in doubt, the plant's identity should be confirmed by a knowledgeable individual and/or by consulting appropriate books.

Distribution

Osage orange is native to the south-central United States where it occurs naturally in Arkansas, Texas, Oklahoma, and perhaps Louisiana. It was introduced early into Missouri to be used for windbreaks, railroad ties, and for fencing cattle pastures. When planted close together in a row, the thorns make a barrier to cattle, hence Osage orange is described as a "living" fence. Osage orange frequently escapes from hedgerows. It has become naturalized and widespread in the Central States and undoubtedly occurs in all Missouri counties today.

Habitat

Osage orange typically occurs in open sunny areas and can grow in a variety of soils. It is most frequently found growing in hedgerows or in pastures, but also occurs in disturbed forests and on river banks. Osage orange dominates large areas of abandoned pastureland in the Glaciated Plains, the Osage Plains and the Springfield Plateau regions of Missouri.

Life History

A single female Osage orange tree can produce many fruits, each containing many seeds. Although fruits are quite large, the seeds do get dispersed over long distances by animals that eat them. Osage orange can reproduce from root sprouts.

Effects Upon Natural Areas

Osage orange is a native species that can become a nuisance in prairies and savannas. It also invades forest communities, usually as a result of past disturbance, such as grazing.

Control Recommendations

Recommended Practices in Natural Communities of High Quality

Initial effort in areas of heavy infestation

Cutting and/or burning offer the best solutions for control. Cutting during summer months (June-August) should provide the best results, and two cuttings in one year are more effective than one. Summer cutting affects the plant when its root reserves are low and the possibility of adverse weather during the fall and winter may further harm the plants. Repeated cutting may be necessary to control Osage orange completely because it resprouts from the stump and by root suckers, and may cover large areas vegetatively. Cutting is most feasible with smaller plants.

Although girdling has not been tried as yet on Osage orange, it may prove successful on smaller trees that do not have thick bark. Older trees have quite thick bark, making girdling difficult. For girdling, the phloem should be removed without damaging the xylem. The xylem should be left to continue to conduct root reserves into the crown, thereby diminishing the capacity of the tree to resprout. The girdles should be checked every several weeks at first to make sure that bark does not develop over the cut area. Girdling can be done with an ax, saw, or chainsaw. Two parallel cuts 3 to 4 inches apart, cutting through the bark slightly deeper than the cambium, are needed. The bark is knocked off using a blunt object like the head of an ax. Periodic prescribed burning will help keep young Osage orange plants from becoming established. Burning in conjunction with cutting works well on small plants. Large Osage orange trees are resistant to fire and will need another control method such as girdling or cutting.

All cutting or girdling practices, without herbicide treatment, will result initially in the development of masses of vigorous sprouts which are extremely difficult and hazardous to handle due to their axillary spines. The tips of these spines are brittle and may remain embedded when the spines are extracted from puncture wounds. Workers should take extra precautions to protect their eyes, hands, arms, knees, and feet when handling these sprouts. A cut-surface treatment with herbicide, as described below, is recommended to minimize sprouting.

Recommended Practices on Lands Other Than High-Quality Natural Areas

Initial efforts in areas of light infestation

Same as given above for heavily infested areas.

Maintenance control

Periodic prescribed burning will hinder establishment of young Osage orange plants. Burning or chipping also will be required to reduce the thorny debris following cutting, since the spines as well as the heartwood are very decay resistant.

Initial effort in areas of heavy infestation

Same as given above for heavily infested areas except that labor-saving herbicides discussed below may be used when manpower is limited. Triclopyr herbicide (trade name Garlon 4 or 3A) is effective as a bark treatment or cut-surface treatment. Undiluted Garlon 4 can be applied in a thin stream to all sides of the stem, 6 inches above the base of the plant. This only works on trees with stems less than 6 inches in diameter. A narrow band of Garlon 4 encircling the stem is needed for control. This method should not be used in high-quality natural areas because the diesel fuel may kill vegetation around the tree. Cut-surface treatment with Garlon 3A, a selective translocated herbicide, effectively controls Osage orange. A diluted solution of Garlon 3A (50-percent solution in water) can be sprayed on cut surfaces or else wiped on the cut surface using a sponge applicator. Either a stump or girdle can be used for the cut surface. Girdles can be made rapidly using a chain saw. Application should be as soon as possible, and no later than two to three hours after cutting. Cut-surface application can be made during any season of the year, but application during the dormant season reduces the potential for injury to other plants due to drift.

Basal bark treatment with Garlon 4 also is effective. Two or 2 1/2 ounces of Garlon 4 is added to 1 gallon of diesel fuel. This mixture is sprayed, using a hand sprayer, to the basal portion of the tree trunk. Spray to a height of 12 to 15 inches (30.5 to 38.1 cm). Thorough spraying is necessary. This method should only be used in less sensitive areas because runoff of diesel fuel and herbicide may harm nearby plants.

Use of Triclopyr is best done in the dormant season to lessen damage to non-target plants. Great care should be exercised to avoid getting any of the mixtures on the ground near the target plant since some non-target species may be harmed. Avoid using Triclopyr if rain is forecast for the following one to four days, otherwise run off will harm non-target species. By law, herbicides only may be applied as per label directions. Osage orange seems to be very sensitive to Triclopyr, therefore very small amounts can be used, lessening the possible harm to non-target plants.

Initial efforts in areas of light infestation

Same as given above for heavily infested areas. Periodic prescribed burning controls seedlings and saplings.

Maintenance control

Periodic prescribed burning will hinder establishment of young Osage orange plants.

Failed or Ineffective Practices

No biological controls are known that are feasible in natural areas.

Key Messages: 

Missourians care about conserving forests, fish and wildlife.

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