Recently, cucurbit yellow vine decline, a relatively new disease in the Northeast, was confirmed in my pumpkin trial as well as in a commercial pumpkin field in PA. This disease was first detected in Oklahoma and Texas in 1988 and has since been confirmed in the Southeast region of the U.S. In the Northeast, it was confirmed in Massachusetts in 2003 but has not been seen since and has also been suspected in Ohio. Although previously suspected in PA, this is the first confirmation of the disease statewide.
This disease is caused by the bacteria, Serratia marcescens, which is vectored by the squash bug (Anasa tristis). The symptoms are similar to bacterial wilt which is transmitted by the cucumber beetle but disease progression is much more rapid. The plants can wilt and turn yellow almost overnight usually 10 to 14 days before the fruit is mature. Cross-sectioning of the crown can reveal discoloration of the phloem tissue which has become colonized by the bacteria.
The key to managing CYVD is early detection and management of the squash bug in the nymphal stages. Similar to bacterial wilt, once the bacteria are inside the plant there is little that can be done to prevent the plant from dying. The squash bugs themselves can also cause direct damage by using the piercing-sucking mouthparts to suck the sap out of the leaves causing them to wilt and collapse. Intense feeding can cause the entire leaf to collapse. Although the squash bug is considered a pest on all cucurbits, it prefers squash and pumpkins and CYVD is primarily a problem on these cucurbit crops as well.
It is important to scout for squash bug early by looking for the iridescent bronze colored eggs on the lower leaf surface. The egg masses are laid in a diamond or V-shaped pattern and can consist of up to 20 eggs. The eggs will hatch in one to two weeks and then take an additional four to six weeks to go through five instars to become adults. All life stages may be found on the same plant because the female lays eggs over a long period of time. The unmated adults will overwinter in plant debris or along edges of fields also harboring the bacteria overwinter. The next season these adults move into the crop and transmit the bacteria.
The action threshold for squash bug is one egg mass per plant during flowering. It is important to manage them early in the season before the populations are large and there are a greater proportion of adults which are more difficult to manage. Also as the crop becomes larger it can be more difficult to get foliar insecticides into the crop canopy. The two most critical points for the host is at the young seedling stage and at flowering. Chemical treatments should be directed towards the nymph stages and application coverage is critical since they tend to hide.
Mowing weeds and managing vegetation around field edges will reduce potential overwintering sites for the squash bugs. Maintaining a healthy actively growing crop through optimal fertilizing and irrigating will also help reduce squash bug feeding. Rotate cucurbit fields as far apart as possible.