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Melons & watermelon

Most bugs on melon plants arrive in the same few weeks, between sowing and the first flowers, and the first of them decides a lot. Striped and spotted cucumber beetles chew the seedlings and carry bacterial wilt into their feeding wounds. Muskmelon and cantaloupe are susceptible, so Minnesota Extension acts at half a beetle per seedling. Watermelon is not affected by the disease (UF/IFAS), and Wisconsin tolerates five beetles per plant on it. Row cover is the defence Minnesota, Wisconsin and Clemson all recommend, and Minnesota and Wisconsin say to take it off when the plants flower so bees can pollinate.

Later in the summer the damage moves to the leaves and the rind. Clemson calls spider mites a serious problem on watermelon and cantaloupe in hot, dry weather, and melon aphids become a problem once the vines start to run, carrying mosaic viruses. In the South and West, silverleaf whitefly and pickleworm join in. Caterpillars such as beet armyworm and cabbage looper chew pale blotches into watermelon rinds, which UF/IFAS calls the rindworm complex. The squash vine borer is the one squash pest melon growers can mostly ignore: Minnesota and Maryland say it rarely attacks melons.

crop context · cantaloupe vines in flower, early summer

Common melon and watermelon pests, in the order you meet them

SEEDLINGS · MAY–JUNE

Striped cucumber beetle

Spreads bacterial wilt into muskmelon and cantaloupe. Watermelon is not affected, so it tolerates more beetles.

ReleaseGround beetlesNothing to release — ground beetles and wolf spiders reduce numbers (JIPM)
JULY IN THE NORTH

Spotted cucumber beetle

Feeds on leaves, flowers and fruit and also carries bacterial wilt. Most abundant in the South.

ReleaseBraconid waspsWild — nothing to release (UF/IFAS lists braconids among its enemies)
JUNE–JULY

Squash bug

Sources disagree on melons: UC IPM ranks watermelon among the worst hit, but bugs survive better on squash.

ReleaseTachinid fliesWild — keep nectar plants near the crop, no broad-spectrum sprays
HOT, DRY SPELLS

Two-spotted spider mite

Pale yellow and reddish-brown spotting in hot, dry weather. Clemson says it can kill or stunt plants.

ReleasePhytoseiulus persimilis2–50 /m² per release (Koppert); UC IPM says releases are untested in cucurbits
ONCE VINES RUN

Melon aphid

Colonies under the leaves, and mosaic viruses, which no natural enemy slows.

ReleaseHoverfliesWild — attract adults with open flowers
LATE SUMMER · SOUTH & WEST

Silverleaf whitefly

Honeydew on the fruit, and viruses, including the one behind watermelon vine decline in Florida.

ReleaseBig-eyed bugsWild — nothing to release; spare them by avoiding broad-spectrum sprays
SUMMER · SOUTH

Pickleworm

Bores into flowers and scars cantaloupe rinds. Watermelon is rarely attacked.

ReleaseGround beetlesNothing to release — no natural enemy reliably suppresses it (UF/IFAS)

Season calendar

TEMPERATE US · OUTDOOR MELONS · QUALITATIVE
JFMAMJJASOND
Striped cucumber beetleJan: QuietFeb: QuietMar: QuietApr: QuietMay: BuildingJun: Pest pressure highJul: BuildingAug: BuildingSep: QuietOct: QuietNov: QuietDec: Quiet
Spotted cucumber beetleJan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: BuildingJul: Pest pressure highAug: Pest pressure highSep: BuildingOct: QuietNov: QuietDec: Quiet
Squash bugJan: QuietFeb: QuietMar: QuietApr: QuietMay: BuildingJun: Pest pressure highJul: Pest pressure highAug: BuildingSep: BuildingOct: QuietNov: QuietDec: Quiet
Spider miteJan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: BuildingJul: Pest pressure highAug: Pest pressure highSep: BuildingOct: QuietNov: QuietDec: Quiet
Melon aphidJan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: BuildingJul: BuildingAug: BuildingSep: Pest pressure highOct: Pest pressure highNov: QuietDec: Quiet
Silverleaf whitefly (South & West)Jan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: QuietJul: BuildingAug: Pest pressure highSep: Pest pressure highOct: Pest pressure highNov: BuildingDec: Quiet
Pickleworm (South)Jan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: BuildingJul: BuildingAug: Pest pressure highSep: Pest pressure highOct: BuildingNov: QuietDec: Quiet

Starter program

No release protects melon seedlings from cucumber beetles; row cover does that. The one purchase that can pay is predatory mites once spider mites are confirmed, and even that has not been tested in outdoor cucurbits.

  1. AT SOWINGGround beetlesNothing to release. Keep the crop under row cover until it flowers; on cantaloupe and muskmelon this is the main defence against bacterial wilt. A thick straw mulch around the plants makes it harder for cucumber beetles to lay eggs.
  2. SUMMERTachinid fliesNothing to release. Keep nectar plants near the vines and avoid broad-spectrum sprays; Trichopoda parasitises squash bugs.
  3. ON FINDING MITESPhytoseiulus persimilis2–50 /m² per release (Koppert), repeated once or twice at weekly intervals. UC IPM notes that releases have not been researched in cucurbits, and that once runners pass about 14 in (35 cm), natural enemies usually keep mites in check. Koppert says the predator stops working above 86 °F (30 °C) and struggles below 70% relative humidity.
  4. LATE SUMMERHoverfliesNothing to release. Keep open flowers near the bed and leave aphid colonies that already have larvae in them. They reduce aphids but not virus spread, so use reflective mulch while the plants are small.

Setting up the garden

Most melon pest control is done at planting, before a beetle has landed.

Cover until the first flowers

Row cover keeps cucumber beetles off the seedlings. Take it off when flowering starts: melons need bees to set fruit.

Pick less attractive cantaloupes

Wisconsin Extension names 'Makdimon' and 'Rocky Sweet' as cantaloupes that attract fewer cucumber beetles.

Lay reflective mulch early

UF/IFAS says reflective mulch can slow aphid infestation while plants are small and help against whiteflies early in the season, before the vines cover it.

Keep sprays out of the flowers

Maryland Extension advises avoiding pesticides, especially during bloom, to protect the bees that pollinate melons. Fewer sprays also spare the predators that hold spider mites down (UC IPM).