Pest Management Strategic Plan for Watermelons in Delaware, Maryland, New Jersey, North Carolina and Virginia

Weeds

Weeds cause economic loss in watermelons in many ways. Some of these are 1) competition for nutrients, water and light will reduce yields 2) weed foliage may intercept the spray of fungicides and insecticides and prevent contact with the watermelon foliage and fruit 3) harvesting crews cannot find the watermelons covered by weeds and this slows or prevents harvest 4) weed leaves or other plant parts that contact watermelon rind usually create an imprint on the rind and make the melon unsaleable due to a visual defect in the rind.

CULTURAL CONTROL

Cultivation
Cultivations are an essential component of watermelon production, because herbicides alone seldom control all the weed seeds or all weed species. When weed escapes occur, cultivation is preferable to hoeing or applying post-emergence herbicides. Cultivation is not commonly an option in plasticulture watermelon, but is used extensively in bareground watermelons.

Crop Rotations
Soil persistence (carryover) from herbicides used on previous crops may cause injury to watermelons. Advance planning in herbicide selections is essential to safely rotate watermelons after most agronomic crops and some vegetable crops. The herbicides Scepter, Pursuit and Classic have a great potential for vine crop injury in the next season. The labels for atrazine and simazine (Princep) prohibit most vegetable crop for over 12 months; however, experience has shown that rates of less than 2.0 lb ai/A total triazines do not cause vine crop injury the next year. Metribuzin (Sencor or Lexone), which is a triazine, does not cause carry-over injury to vine crops.

The only safe preemergence herbicides to use on soybeans prior to watermelons are linuron (Lorox, Linex), alachlor (MicroTech, Partner) or metolachlor (Dual, Magnum). Also the dinitrioaniline herbicides trifluralin (Treflan, Trilan) and pendimethalin (Prowl) might have a residual effect on watermelons, but do not carry over to the next year. The postemergence soybean herbicides acifluorfen (Blazer), bentazon (Basagran), lactofen (Cobra), thifensulfuron (Pinnacle) and Roundup would not affect watermelons in the next year.

CHEMICAL CONTROL – HERBICIDES

Of the pesticides listed in this document, bensulide is an organophosphate. The rest are neither an OP, Carbamate, or B1 B2 potential carcinogen.

I. Preplant incorporated or Preemergence Herbicides - Seeded and Transplanted Watermelon

Prefar may be applied preplant incorporated or preemergence. If applied preemergence, rainfall or irrigation must occur prior to weed emergence to activate the herbicide. Prefar may be tank mixed with most other herbicides to control more weed species. Watermelons may be transplanted directly through the Prefar herbicide zone on the soil surface or preplant incorporated. Surface applied or shallowly incorporated combinations of Prefar plus Command are acceptable for transplanted watermelons.

Command 3ME now has a Section 3 label.  Command 3ME is for preemergence applications, not preplant incorporated. Command 3ME does not have the volatility concerns that Command 4EC had which would cause severe damage to off-target crops or vegetation from drift during application.  Command provides good to excellent control of annual grasses, lambsquarters, purslane and ragweed. Jimsonweed is usually suppressed by Command. Pigweed control is not acceptable with Command alone and combinations with Sinbar, Curbit or Prefar greatly improve control. Command does not control morningglories.

Alanap may cause temporary stunting, especially if cool wet weather follows application.  Alanap is applied preemergence or preplant incorporated for seeded and transplanted watermelon. Alanap should be combined with other herbicides to improve weed control. Although Alanap does not control grasses it may improve control of cocklebur, jimsonweed and ragweed. Also, Alanap may improve weed control when combined with Prefar, Curbit or Command.

 (North Carolina) Labeled for preplant application to non-selectively kill emerged weeds before watermelon emergence. This herbicide is used on little of the watermelon acreage. This low usage is probably because producers rely on tillage to kill sprouted weed seed and emerged weeds. Killing weeds prior to watermelon planting is critical since weeds that survive the planting operation can drastically reduce watermelon yield. Certain formulations of glyphosate are also registered preplant in watermelon for non-selective kill of emerged weeds. The label lists precautions on when growers can plant after glyphosate application.

II. Preemergence Herbicides

Preemergence application to the soil surface only, after seeding or before transplanting. Sinbar was registered annually in 1996 and 1997 for preemergence application on watermelons in Delmarva as a Section 18 Emergency Registration . The IR-4 Project has a program to obtain a national registration for Sinbar on watermelon. Seeded watermelon are tolerant to low rates of Sinbar. Transplanted watermelons have shown moderate tolerance to Sinbar in a few studies, and growers should evaluate this use with their own plants and soil type. Sinbar should be applied to the soil surface before transplanting.

Sinbar will provide excellent control of morningglory species. Most morningglories will emerge but the leaves will become brown (necrotic) and die. Other weeds controlled are ragweed, carpetweed lambsquarters, jimsonweed and cocklebur. Pigweed may be suppressed but only fair control is obtained for pigweed and combinations with Curbit or Prefar are necessary for control. The low rates of Sinbar do not affect crops after watermelons.

Applied preemergence only for seeded watermelon. Do not use on transplants. To control annual grasses and certain broadleaf weeds. Curbit can be used at a 3 pint/A on soils with approximately 2% O.M. or more, especially if manures have been applied. Control of many broadleaf weeds, including pigweed sp., common lambsquarter, jimsonweed, morningglory sp., ragweed sp., mustard sp., and others may not be acceptable. Dry weather following application may reduce weed control. Cultivate to control tolerant weeds or if rainfall or irrigation does not occur prior to weed emergence. Curbit should be combined with herbicides such as Command, Prefar, and Sinbar.

To prevent injury: 1) DO NOT preplant incorporate. 2) DO NOT apply under plastic mulch or tunnels. 3) DO NOT use on transplanted watermelon. 4) DO NOT use when soils are cold or wet.

III. Postemergence Herbicides

With oil concentrate postemergence to control annual grasses and certain perennial grasses. The use of oil concentrate may increase the risk of crop injury when hot or humid conditions prevail. To reduce the risk of crop injury, omit additives or switch to nonionic surfactant when grasses are small and soil moisture is adequate. Control may be reduced if grasses are large or if hot, dry weather or drought conditions occur. For best results, treat annual grasses when they are actively growing and before tillers are present. Poast provides excellent control of fall panicum, goosegrass, lovegrass, and foxtails. Crabgrass smooth and large should be sprayed when relatively small for effective control. Generally Poast is most effective if applied 3 to 5 days prior to cultivation because it will weaken grasses and make them more vulnerable to killing by cultivation. A second application may be made for grasses that are difficult to control or for new flushes of germinating grasses. Poast will control johnsongrass and shattercane and it is also effective for control of volunteer rye and wheat. Repeated applications may be needed to control certain perennial grasses. Yellow nutsedge, wild onion, or broadleaf weeds will not be controlled with Poast. Do not tank-mix Poast with pesticides or apply within 2 to 3 days of any other pesticide unless labeled, because the risk of crop injury may be increased or reduced control of grasses may occur. Observe a minimum preharvest interval of 14 days and apply no more than 3 pints per acre in one season. Use 20 gal/A spray volume or less per acre.

Our studies indicate that if grasses are controlled in the first six weeks after planting, watermelon yields will not be reduced by competition from the grasses. Therefore, Poast applications later than six weeks after seeding would be unnecessary provided grasses had been controlled during the initial six week period. Exceptions would be for crabgrass or johnsongrass that may require two applications.

Applied broadcast postemergence to watermelons may be applied anytime up through early flowering. Alanap will stop the growth of many weeds for 4 to 5 weeks. Weeds suppressed are ragweed, all morningglory species, purslane, lambsquarters and pigweed. Slight watermelon leaf crinkling may occur, but it is a temporary condition.

DPCA can be applied 5-6 weeks after planting, and is useful in fields that develop severe common purslane infestations during the summer.  DPCA is an option for application when watermelon has at least 4 to 5 true leaves. It is registered in bareground culture and has potential to give late season weed control. It has only had limited used in North Carolina.

Trifluralin is not recommended in the mid-Atlantic states.

Is registered in watermelon for postemergence control of yellow and purple nutsedge and broadleaf weeds (wild mustard, wild radish, common ragweed, galinsoga, and cocklebur). It is most effective postemergence on yellow and purple nutsedge compared to preemergence application. It can only be used in the middles between rows as it has potential to injure watermelon if applied over the top of watermelon plants.

Certain formulations of glyphosate are registered for weed control in row middles of watermelon in North Carolina, but they are not recommended in the mid-Atlantic states. This herbicide controls most plants; thus must not contact the crop. It has had limited used in North Carolina due to the potential for crop injury.

PHI - 14 days. Postemergence.  Select 2EC requires oil concentrate to control many annual and certain perennial grasses, including annual bluegrass. However, it will not consistently control goosegrass. The use of oil concentrate may increase the risk of crop injury when hot or humid conditions prevail. To reduce the risk of crop injury, omit additives or switch to nonionic surfactant -- SelectMax 0.97EC can be applied with nonionic surfactant which reduces the risk of crop injury during “soft” growing conditions -- when grasses are small and soil moisture is adequate. Control may be reduced if grasses are large or if hot, dry weather or drought conditions occur. For best results, treat annual grasses when they are actively growing and before tillers are present. Repeated applications may be needed to control certain perennial grasses.. Yellow nutsedge, wild onion, or broadleaf weeds will not be controlled. Do NOT tank-mix with or apply within 2 to 3 days of any other pesticide unless labeled, as the risk of crop injury may be increased, or reduced control of grasses may result. REI - 24 hours.

IV. Post-Directed Herbicides

Use a directed shielded applicator and spray at very low pressure of approximately 20 psi or less. Apply for the control of existing weeds between rows of watermelons. Gramoxone provides contact kill of most all broadleaf weeds and small grasses. Grasses may recover from Gramoxone contact injury. Gramoxone will kill most grasses under 2 to 4 inches height, but larger grasses may recover and continue to grow. This application may be made to soil between the rows of watermelon on bare ground and on the soil between plastic mulch strips.

V. Contact Herbicides

1. Delayed Preemergence

Apply Gramoxone Inteon 2SC just before emergence of crop to control early germinating weeds. Use wetting agent as directed on label. Emerged melon seedlings will be killed.

2. Pre Plant Application

for control of annual weeds. Apply 3 days before seeding or transplanting. Used for the control of most annual weeds and cereal cover crops.

VI. Postharvest

A Special Local-Needs 24(c) label has been approved for the use of Gramoxone Inteon 2SC as a broadcast spray after the last harvest. Add nonionic surfactant according to the labeled instructions. This application method may be used to prepare plastic mulch for replanting, or to aid in the removal of the mulch.