Crop Profile for Watermelon in Arkansas

• State Rank: 14th
• Percentage of U.S. Production: Less than 2%
• Total acres grown: 3,600 acres (estimated )
• Cash Value: $ 3.5 to 6 million (estimated )
• Production Regions: Watermelon production is distributed throughout Arkansas with the greatest concentration of growers in North Eastern Arkansas and in South East Arkansas in Bradley, Drew, and Ashley Counties.

The watermelon, Citrillus vulgaris, is a member of the Curcurbitaceae or gourd family. Watermelon is a very tender annual. Many growers in Arkansas now produce melons using the plasticulture production system. Transplants are planted in early spring from April 15 to May 15 depending on soil temperature and location in the state, in single rows at densities of approximately 1000 plants per acre on raised beds that are covered with black plastic mulch at 24 -48 inches apart and 72-96 inches between rows. Watermelons are either seeded or transplanted for an earlier crop.

Watermelons grow best on a sandy, loam soil, pH of 5.5-7.2 although yields on clay soils with good management are higher. Melons mature in 70-130 days depending on the variety and soil temperature.

Supplying bees for pollination is essential for consistent production. Most growers will realize noticeable increases in yield from placing one strong colony of bees every 2 acres in or alongside the field when blooms begin to appear.

Approximately 10-15" of moisture per season is required for watermelon production with a steady moisture supply of 1-2" every 10-14 days required. Irrigation should be stopped approximately 10-14 days prior to anticipated maturity (onset of flesh color). Key stages of irrigation are establishment and fruit set. Drip irrigation and fertigation is used on 50% of the acres of melon produced.

Melon transplants are normally planted in the spring (April 15 to May 15) into plastic covered beds. Approximately 50% of the acreage uses transplants planting is by hand assisted means. The other 50 % of the acreage is direct seeded. Seed is hill dropped by hand or seeded by machine

Preemergent herbicide applications are applied to the beds of mulched melons. These applications are made in early spring, primarily with tractor mounted spray equipment.

Postemergence herbicide applications are made to the beds of traditionally grown melons and the row middles of plastic covered beds in early summer and occasionally after harvest primarily with tractor mounted sprayers although backpack sprayers are occasionally used. Hand labor is used to train the vines on the plastic (May to June).

Insecticides and fungicides are applied from early spring up to harvest primarily with airblast sprayers or boom sprayers.

The entire melon crop is hand-harvested (July-August). The melon plants are normally removed after harvest as well as the plastic mulch. This is all done by hand.

Both species of cucumber beetles are known to infest watermelon fields. Beetles overwinter in nearby hedgerows and woodlands feeding on alternate weed hosts in the early spring. As soon as melons germinate in March and April, beetles migrate to the field and begin feeding on young seedlings. Although most watermelon cultivars have good bacterial wilt resistance, heavy beetle populations (greater than 5 per plant) can severely affect stand establishment during the cotyledon stage. Once the first three leaves are established, plants generally compensate for damage through vigorous growth.

Controls

Aphids (Aphis gossypii)

Aphids feed mainly on the undersides of the leaves causing cupping of leaves, leaf distortion, plant stunting, and a reduction in the quality and quantity of fruit. Infestations are usually higher in hot, dry summers following cool springs which reduce the efficiency of natural enemies. In addition, over fertilization with nitrogen can increase aphid populations. Honeydew secreted by aphids supports growth of sooty mold on leaves and fruit. Aphids may transmit viruses.

Spider Mites (Tetranychus spp.)

Spider mites can be a serious pest of watermelons, especially during hot, dry weather. Infested plants appear yellow and become visible from a distance. Mites are primarily found on the undersides of leaves making the leaves appear tan or yellow and have a "crusty appearance". Mites feed on the plant sap and can defoliate vines in a few weeks in hot, dry weather. Defoliated plants tend to yield small, poor quality fruit.

Squash bugs feed on plant phloem and xylem. Both adults and nymphs feed on plants. Squash bugs can occur in large numbers, weakening or killing plants. Damaged leaves appear grayish and may wilt and die. Adults tend to occur around the base of the plant near the ground, and may be abundant in fields with plastic mulch.

Successful management of squash bugs is based on prohibiting early season population increases.

Key weeds that are common problems for Arkansas producers are Smooth pigweed (Amaranthus hybridus), Palmer amaranth (Amaranthus palmeri), Lambsquarters (Chenopodium album), Common cocklebur (Xanthium strumarium), Velvetleaf (Abutilon theophrasti), Purslane (Portulaca oleracea) and Carpetweed (Mollugo verticillata). Noxious weeds such as Johnsongrass (Sorghum halepense) require periodic control.

In general, management of weeds is accomplished through a thorough tillage of the seedbed after which black plastic is laid down. A pre-emergence herbicide is used in between rows and cultivation or post applications of herbicides are used for in-season weed control.

Prevention Strategy
Tillage and black plastic provide significant weed control during the season.

Avoidance Strategy
Crop rotation is very important in weed management. Excellent weed control in cotton the year preceding watermelons is highly desired by growers.

Monitoring Strategy
Fields are scouted by producers for weed infestations and tillage operations and/or post-emergence herbicide applications are timed accordingly.

Suppression Strategy
Approximately 95% of watermelon fields are treated with herbicides to suppress weed competition.

• Trifluralin (Treflan 4E) Applied to 85% of acres by ground at an average rate of 1 lb a.i. per acre. Typically included in the spring burndown. Also used as needed in spot applications. . PHI – 60 days. REI – 12 hours.
• Naptalam (Alanap-L) Applied to >50% of the acres as pre and post-emergence application at an average rate of 3.0 lb a.i. per acre. Most often mixed with Bensulide. PHI – N/A. REI – 48 hours.
• Bensulide (Prefar) Applied to >50% of the acres as a pre and post-emergence application at an average rate of 1.25 lb a.i. per acre. Most often mixed with Alanap-L. PHI – N/A. REI – 12 hours.
• Sethoxydim (Poast 1.5 EC) Applied to 95% of the acres as post-emergence application for the control of grassy weeds. The average application rate is 0.30 lb a.i. per acre. PHI – 14 days. REI – 12 hours.
• Glyphosate (Roundup Ultra) Applied to 50% of the acres as a spot treatment for weedy escapes. The average application rate is 1 lb a.i. per acre. PHI – N/A. REI – 4 hours.
• Paraquat (Gramoxone Extra 2.5E) Applied to 50% of the acres as a spot treatment for weedy escapes. The average application rate is 0.63 lb a.i. per acre. PHI – N/A. REI – 24 hours.
• Ethalfluralin (Curbit EC) Applied to 10% of the acres. It is often used as a rescue in fields with heavy weed pressure. It is a very effective broadleaf herbicide but also very expensive. PHI – N/A. REI – 24 hours.

Fusarium Wilt (Fusarium niveum)

Fusarium wilt is caused by a fungus that lives in the soil and penetrates the roots. Symptoms are a brown discoloration of the vascular system of roots and stems, followed by a wilting and death of the plant.

Anthracnose (Colletotrichum orbiculare)

Anthracnose attacks all above-ground parts of watermelon plants. It can completely kill vines before the fruit matures, cause lesions on the fruit which can ruin them in the field, or results in loss to decay in transit. The symptoms include irregular, brown to black, dry leaf spots, eventually causing the leaf to shrivel up and die. On the fruit, sunken, circular to irregular lesions occur from pinpoint size to one inch or more in diameter. Elongate stem and petiole lesions occur. Spores of the fungus are produced on lesions that may rapidly spread the infection following rainy weather. The fungus overwinters in decaying vines and on seed from diseased fruit. It is the most important and destructive foliar disease in Arkansas.

Alternaria Leaf Blight (Alternaria cucumerina)

This disease causes leaf spots and defoliation. It overwinters in infected plant debris in the soil and seed. It is a relatively minor disease.

Cercospora Leaf Spot (Cercospora citrullina)

This disease causes small, circular, leaf spots that can cause defoliation of vines under severe disease pressure. Normally it is of minor importance.

Downy Mildew (Pseudoperonospora cubensis)

This disease causes large brown blotches on leaves and rapidly defoliates vines. Stems and fruit are not affected. It is favored by cool, wet nights, and warm humid days. It is mainly important in late-season (fall) production.

Gummy Stem Blight (Didymella bryoniae)

The disease attacks only the leaves and stems of watermelon. This fungus also overwinters in infected plant debris in the soil and seed. It can be a serious disease in Arkansas.

Bacterial Fruit Blotch (Acidovorax avena subsp. citrulli)

Causes brown spots on leaves that are of minor importance. Causes large water-soaked, greasy areas on upper part of fruit which renders fruit unmarketable. The disease is seedborne and can survives in crop debris and volunteer melons. Only seen in transplant melons and is a minor disease.

Profile Compiled By:

1. Andersen, Dr. Craig R., Extension Horticulturist – Vegetables. MP-128, Vegetable Gardening in Arkansas. University of Arkansas, Division of Agriculture, Cooperative Extension Service, 1997.

2. MP 144, 2003 Insecticide Recommendations for Arkansas. University of Arkansas, Division of Agriculture, Cooperative Extension Service, 2003.

3. MP-44, 2003 Recommended Chemicals for Weed and Brush Control. University of Arkansas, Division of Agriculture, Cooperative Extension Service, 2003

4. MP-154 Plant Disease Control Handbook. University of Arkansas, Division of Agriculture, Cooperative Extension Service, 1991.

5. Statistics of Vegetables and Melons, USDA, National Agricultural Statistics Service, Crops Branch, 1999.

6. USDA, National Statistics Service, Census of Agriculture-Arkansas, 1997.

7. Crop Profile for Watermelons in Missouri. March 2000. USDA Pest Management Center.