Cucumber Beetles

Striped cucumber beetles (SCB) adults have three black stripes, a yellow thorax, and a black head. They cause foliar damage as they feed and can be a vector for devastating diseases like bacterial wilt and squash mosaic virus. Adult beetles may also congregate in flowers, potentially damaging fruit.

Spotted cucumber beetles, also known as southern corn rootworm (SCR) are often found in cucurbit flowers. Adults are yellowish green with 12 black spots on their back.  They feed on a wide range of crops and weeds and rarely build up to damaging levels in New England, and when they do, they largely pose a threat to younger plants. Adults cause direct feeding damage to cotyledons, leaves and the base of the stem, while larvae feed on plant roots. Their feeding is also a source for spreading bacterial wilt.

Cucumbers and muskmelons are highly susceptible to bacterial wilt. Treat these crops if one cucumber beetle is found for every two plants. Butternut squash, watermelon, and most pumpkins are less susceptible to bacterial wilt and can tolerate 1-2 beetles per plant. There aren’t many bee-friendly options for chemical control, so get populations under control early on to prevent the need to spray during flowering or consider spraying in the evening after bees have stopped foraging. Learn more about reducing the risk to pollinators.

The most effective OMRI-listed material is pyrethrin (e.g. Pyganic). Small plants can also be protected using kaolin clay (e.g. Surround), which needs to be reapplied to protect new growth. If you are applying a contact spray, target adult beetles in the evening when they are less active. For crops most susceptible to bacteria wilt, a systemic insecticide may be more effective. Systemic insecticides can be applied to the seed or the seedling root zone during or after planting/transplanting.

See the New England Vegetable Management Guide for more information on insect control for cucurbit crops.

Squash Bugs

Squash bugs are most attracted to zucchini, yellow summer squash, and pumpkins. Both adults and nymphs feed on plant tissue and can cause the whole plant to wilt. They will also feed on fruits resulting in scarring and impacting their marketability. Symptoms like plant wilt, leaf yellowing, and plant stunting can sometimes be mistaken for squash vine borer. Inspect the stem for an entry hole and frass from the borer to differentiate. Squash bugs can be vectors for cucurbit yellow vine decline, a bacterial disease that has been found in isolated places in CT and MA.

Scout the undersides of leaves for squash bug adults and eggs and treat if egg masses exceed 1 per plant. Adults often hide around the base of the plant or under plastic mulch, making them hard to target with sprays. Eggs are usually deposited on the leaves in an organized, neatly spaced pattern, in groups of 10 to 20. Time squash bug sprays to kill young nymphs which are easiest to control. Thorough coverage is necessary. As emergence often coincides with the bloom period, treat late in the day to reduce risk to bees and select products with lower bee toxicity.

See the New England Vegetable Management Guide for a page on insect control for pumpkin, squash and gourds for spray options.

Angular Leaf Spot

All cucurbits are susceptible to angular leaf spot, but it is most commonly seen on cucumbers. It appears early in the season because it is seed-borne. Symptoms include small, round, water-soaked spots on the leaf tissue that expand until they are confined by veins, giving them the characteristic angular appearance. 

Under moist conditions, a milky white fluid containing bacterial cells may ooze out of the lesion on the lower leaf surface. These wet-looking spots will dry out and turn yellow-brown, or the dead tissue may fall out of the leaf altogether, leaving a “shot-hole”. Yellowing of the leaf between lesions may occur where disease severity is high. Similarly, water-soaked spots may appear on stems and petioles, drying out to form a whitish crust.

Water-soaked spots may also appear on fruit. These spots are small and dry out to form whitish, chalky spots. They cause internal decay of fruit, and fruit that is infected early may be deformed. Affected plants will grow poorly and produce less fruit. The affected fruit is also unmarketable.

To control the spread of the disease, avoid working in the fields when the foliage is wet. Work in clean sections of the field first and infected sections last to avoid spreading the disease to (so far) unaffected plants. If you catch the disease early, before it is widespread and severe, copper may reduce the spread. However, sprays may not be effective if environmental conditions are conducive to the spread of the disease. Till in residues quickly after harvest to encourage a quick breakdown of infected plant tissue. Bacteria can survive on plant residue as long as it is present, up to two years.

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