By Marissa Schuh, Integrated Pest Management Extension Educator
Many winter squash and pumpkins are ready for harvest already. The dry season has meant that fruit that did get enough water generally look good, though there are still spots where cosmetic issues exist on the fruit.
It's hard out here for a plant. Gif: Marissa Schuh, University of Minnesota Extension.
Depending on the variety, the spiny stems and leaves of cucurbits means some scabbiness is a fact of life. But when is that spot, scab, or speck something to make note of when selecting sites and varieties for next year? Read on for some common issues and things to think about.
Peanut-like scabs? Think Oedema
If you are in a part of the state that got a large amount of rain at the end of August, you may have noticed some pumpkins and squash with scabby growths. I have noticed it in some heirloom, Hubbard type squash especially.
Oedema on acorn squash. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org
Zoom in on an pumpkin with severe oedema. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org
This is not the result of a disease, but of a plant physiological problem. Just like when tomato skins split after a large, sudden rain, the cells of a pumpkin fruit can also rupture. The rupturing and scabbing of individual cells in the pumpkin plant give the fruit a lightly colored, scabby appearance. It is most often seen in the ground spot, but can happen anywhere on the developing fruit.
While the pumpkins are ugly, generally spots with oedema scab over and the fruit holds up. They may break down more quickly than unscarred pumpkins, as the oedema can create openings for opportunistic pathogens.
Thin coating of black mold on otherwise healthy fruit? Aphids.
Aphids feeding on leaves above have secreted honeydew onto a pumpkin fruit. Photo: Marissa Schuh, UMN Extension.
The hot summer with little rainfall promoted aphids, whose numbers can balloon when the weather’s warm and there’s no water to knock them off the plants. Aphids feed on plant juices with a straw-like mouthpart. This is a little bit like drinking from a fire hose, and they can’t digest all the sugary sap they eat. This sap comes out of the insect quickly, and will fall on the leaf or whatever is below. This sometimes ends up creating pumpkins that are covered with the honeydew aphids create, and this sugary honeydew can then get moldy. This sticky mold renders pumpkins unmarketable and is hard to wash off.
Powdery mildew wreaked havoc? Look out for sunburn and damaged handles
Powdery mildew pressure has been high this year, leading to early defoliation in some plantings. Powdery mildew itself does not damage the fruit, but the sun exposure it leads to can. If you are seeing fields completely defoliated, it is a good idea to move pumpkins to a garage, barn, or other shady spot until sale time.
Sunburned areas start white, but quickly become covered in opportunistic fungal infections. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org
Powdery mildew in the handle of a pumpkin. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org
Powdery mildew can also infect the handle of pumpkins, causing it to be weakened and fall off. This makes the pumpkins harder to market, especially if they are a jack-o-lantern type.
Fuzz, molds, and mushy fruit? Take notes and seek diagnosis
If you have an isolated area with pumpkins or squash that have melted down or rotten, it is worth digging in a little deeper for a solid diagnosis. Sending in samples of a pumpkin fruit or plant is not an easy task as they reach their full size, but making sure you know what’s going on is worth it as vining vegetables are an important crop group on many farms.
Phytophthora in acorn squash. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org
If sending something into the disease clinic isn't possible, reach out the UMN extension and we can work on figuring out what is going on.
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