Authors:  Sanju Kunwar, Xavier Martini, Nick Dufault, Bob Hochmuth, Carrie Harmon, Jeff Jones, Mark Warren, Elizabeth Cannon, Tatiana Sanchez-Jones, Emily Beach and Kiersten Fullem, UF/IFAS Extension Specialists and County Agents

If you are growing watermelon, squash, or other cucurbits in North Florida, you are likely already familiar with the squash bug (Anasa tristis). This pest primarily sucks the sap out of cucurbit crops and has become concerning this year due to an exceptionally high density in the field. Squash bugs don’t just damage plants with their feeding but can also act as vectors for transmitting the bacterium that causes Cucurbit Yellow Vine Disease (CYVD).

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Identifying the Culprit

To effectively manage squash bugs, you first have to know what to look for in the field.

• Eggs: Squash bug eggs are bronze to copper in color, somewhat flattened, and elliptical. Females usually lay them in tightly spaced clusters of about 20 on the underside of cucurbit leaves (Figure 1A), though they can occasionally be found on the leaf petioles (Figure 1B).

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• Nymphs: When they hatch, the nymphs are light green and wingless (Figure 2A). As they molt and progress through five instars (life stages), they turn darker gray (Figure 2B). Young nymphs are highly gregarious and tend to cluster together at the base (crown) of the plant, often hiding just beneath the plastic mulch surrounding the planting hole.

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• Adults: The adult squash bug is dark grayish-brown to black, measuring about ½ inch in length) (Figure 3A and 3B)

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The Damage: Anasa Wilt vs. CYVD

Squash bugs are damaging enough on their own. As they pierce the plant’s tissue to suck out sap, they secrete highly toxic saliva. This localized feeding causes the foliage to wilt, blacken, and die – a condition commonly referred to as “anasa wilt.”

However, a newer and more systemic problem has emerged. When squash bugs feed, they can also transmit the bacterium Serratia (specifically Serratia ureilytica or marcescens) directly into the plant. This pathogen is the causal agent of Cucurbit Yellow Vine Disease (CYVD). The UF/IFAS Plant Diagnostic Center in Gainesville recently confirmed the presence of this Serratia bacterium via 16S sequencing from symptomatic plants collected from the field.

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Unlike fungal diseases such as Fusarium wilt, which colonizes the xylem (water-transporting vessels) and causes rapid wilting, the CYVD bacterium clogs the phloem (nutrient-transporting vessels). This results in a striking, distinct yellowing of the entire plant (Figure 4A). Symptoms often start with marginal leaf burn and progress to severe stunting, systemic yellowing, and eventual plant death.   This season, we found detection of the bacterium in the plant was most common in crown tissue; leaf and vine samples were not successful.  Removal of infected plants may slow spread of the disease in the field.

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Management and Control Strategies

Because squash bug adults are difficult to kill with standard insecticides, successful management requires vigilance and timing.

1. Scout early and often: Check the underside of leaves for bronze egg clusters and look around the base (crown) of the plants for nymphs. If you see a single yellowing plant, inspect its base immediately; if squash bugs are present, they are likely the vectors of the CYVD.
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2. Target the nymphs: Chemical control is far more effective against the smaller, younger nymphs, so applying treatments while the bugs are still in their early instar stages may provide better control. Because squash bugs are vectoring a disease, waiting for traditional pest thresholds is not recommended. Our current recommendation is to spray the field perimeter with bifenthrin as soon as adults are found. This early intervention is critical to try to avoid or delay their migration to the center of the field. Pyrethroids (MO 3A) are the class of insecticides with the most products labeled for squash bugs. Other options include butenolides (MOA 4D, Sivanto) and chitin biosynthesis inhibitors (MOA 15, Rimon). Neonicotinoids are also labeled for squash bug but should be applied early in the season to protect pollinators (see next section).
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3. Protect Pollinators: Honeybees and native pollinators are vital for cucurbit fruit set. If you must apply insecticide (like a pyrethroid) during the blooming period, do so late in the evening or after dark when bee activity is minimal. Keep in mind that most of the insecticide will not have broken down by the next day, so bees will still be exposed. Read labels carefully and only apply insecticides that minimize effects to pollinators.
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4. Practice field sanitation: Squash bugs overwinter as adults in crop debris, or in nearby brush. As soon as your harvest is complete, practice clean cultivation by destroying and removing crop residues. This removes their winter shelter, which may help reduce the population that will emerge next spring.
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5. Trap Cropping Strategy: Research has shown that squash bugs are highly attracted to Blue Hubbard squash, a hard winter-type variety. Planting a trap crop of Blue Hubbard on the field edges can draw the bugs away from your cash crop. Then. you can then target your management exclusively on the trap crop. This strategy may be a good alternative option for organic growers who are struggling with limited chemical controls.

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If you suspect you have CYVD or need specific chemical control recommendations for squash bugs tailored to your operation, reach out to your local UF/IFAS County Extension Office.

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