Muskmelon

Melons are highly susceptible to the bacterial wilt these beetles carry, so protect seedlings hardest.

Ragged holes in leaves and flowers, scarred fruit rind, and the beetles themselves - striped or spotted, about a quarter inch - diving into blossoms as you approach.

Hand-pick in the cool early morning when beetles are sluggish; kaolin clay deters feeding; spot-treat heavy pressure at flowering with an evening insecticide application to spare bees. Use only a product labeled for the crop you are treating, follow the label exactly, and observe the pre-harvest interval before you pick. Controlling beetles is really about preventing the wilt they spread.

Row covers from planting until flowering are the single best defense (remove at bloom for pollination); yellow sticky traps; delay-sow past the first beetle surge; clean up crop debris in fall and choose wilt-tolerant varieties.

Small yellow beetles marked with black stripes or spots that chew leaves, flowers, and fruit rind. Their real danger is disease: they carry and spread the bacterium that causes cucurbit bacterial wilt and also transmit mosaic viruses, so even light feeding can be costly.

Muskmelon is one of the most wilt-susceptible cucurbits; a single infected runner usually means the whole vine is doomed.

Individual runners wilting in midday sun and reviving at night, then whole-plant collapse; a cut wilted stem oozes sticky sap that strings into a fine thread when you touch it and pull away.

None - remove and destroy wilting plants before beetles carry the bacteria to healthy vines. Prevention through beetle management is the only real control.

There is no cure, so the whole strategy is beetle control: row covers until flowering, prompt beetle knockdown, and wilt-tolerant varieties. Cucumber beetles carry the bacterium over winter and infect through feeding wounds.

A bacterial disease (Erwinia tracheiphila) spread by cucumber beetles that plugs the plant's water-conducting vessels. Infected vines wilt in the heat, recover overnight at first, then collapse and die. Cucumbers and muskmelons are most susceptible; watermelon is essentially immune.

Melon fusarium (f. sp. melonis) is distinct from the watermelon strain; choose varieties bred with resistance where wilt has appeared.

Older leaves and one whole runner yellowing and wilting while the rest looks healthy, stunting, and a reddish-brown streak in the water-conducting tissue when you slice a wilted stem lengthwise.

None once a plant is infected - remove it and rely on resistant varieties and long rotations. The fungus builds up in soil, so where it appears switch that bed to resistant lines or other crop families.

Resistant varieties and grafted rootstock are the main defense; rotate cucurbits out of infected beds for 5+ years; plant in warm, well-drained soil; raise soil pH toward neutral where wilt is chronic.

A soil-borne fungus (Fusarium oxysporum) that infects roots and plugs the water vessels, yellowing and wilting vines from the base up, often one runner at a time. Host-specific strains attack watermelon, muskmelon, and cucumber separately, and the fungus persists in soil for many years.

Mildew-resistant melon varieties are widely available and worth choosing - losing the leaves late means melons that never sweeten fully and rinds that sunscald. Scout weekly from midsummer and start protecting new growth early, since sprays do nothing for leaves that are already coated.

Round white powdery spots on the upper leaf surfaces that spread and merge until whole leaves look dusted. It usually starts on the oldest, lowest, most shaded leaves and works upward, so check there first. Look at the undersides too, and at stems, buds, and flower stalks, which get coated as it advances. Leaves that yellow, brown, curl, or go crisp and drop early under the coating. New growth that opens small, crumpled, or twisted where the fungus has reached the shoot tips. On plants where it gets onto the fruit, a dull gray film, russeted or scarred skin, and cracking. Late in the season, tiny dark specks scattered through the white felt - that is the fungus setting up to overwinter on the debris.

Start early: sprays protect healthy tissue, they do not clean up leaves that are already coated. Pick off and bin the worst leaves as soon as you see them, and open the plant up by thinning or pruning so air moves through. On anything that regrows quickly, shearing the whole plant back forces a clean flush and beats spraying. If it keeps spreading, potassium bicarbonate, horticultural oil, or neem applied weekly will hold it - cover both leaf surfaces. Sulfur also works, but it burns the foliage of some plants, should never go on in heat, and must not be mixed with or applied close behind an oil spray. Whatever you use must be labeled for the plant you are treating: follow that label and observe its pre-harvest interval on anything you eat. Do not compost badly infected material. Late-season mildew on a plant that is finishing anyway is usually cosmetic; on a crop still filling out it is worth acting on.

Give plants room. Crowding and still air are the biggest single driver, so space at the full recommended distance, thin seedlings properly, and divide or prune out congested growth until air moves through the plant. Full sun and an open position help; deep shade and a still corner against a wall are where it always starts. Water at the base rather than overhead, and water early in the day so nothing stays damp overnight. Keep plants evenly watered - drought stress at the roots leaves them far more susceptible, even though the fungus itself likes dry air. Go easy on nitrogen, since soft lush growth is the most vulnerable. Where resistant varieties exist for what you are growing, choosing one is the single most effective thing you can do on a plant that mildews every year. Clear infected leaves and stems away at the end of the season rather than composting them.

Powdery mildew is a fungal disease that coats leaves - and often stems, buds, and fruit - in a white-to-gray powder that looks like spilled talcum. It is not one fungus but a large family of them, each fairly specialised to its own group of plants, which is why mildew on one crop rarely jumps to an unrelated one beside it. Unlike most leaf diseases it does not need wet leaves: it thrives on warm dry days followed by humid nights, and it takes hold fastest where plants stand crowded in still air or in shade. The coating blocks light, so heavily covered leaves yellow, brown, and drop early. On many plants that is mostly disfiguring and arrives late enough not to matter; where it strips away the leaves a crop still needed to finish, it costs you size, sweetness, and quality.