I love ground cherries (Physalis pruinosa)—but have been experiencing a frustrating problem for the past several years. At some point in the season most (and sometimes all) of the plants will languish, display stunted new foliage, drop fruit prematurely—usually after little to no production—and then wilt and ultimately die. Sometimes necrotic spots will appear on the leaves—though I was never sure whether it was related to the problem or if it was an unrelated foliar disease or cultural issue—, and some of the fruits will display pale spotting/mottling and even slight deformation.
I thought for a while that a soil-borne pathogen might be the cause—maybe verticillium; so this year I took measures to ensure excellent root drainage, planting the ground cherries in a ridge. I also started them earlier this year—on February 15—and up-potted them and grew them out in bigger pots before planting in the garden in May. The idea was that bigger, healthier plants with more root mass would better resist infection. In addition, all plants were inoculated with mycorrhizae and the site dressed with neem cake before planting. It worked . . . for a brief while. One of my plants started wilting a couple of weeks ago and is now in a state of complete collapse. And two more are now following suit. They produced some before taking ill—but that is undoubtedly because they were older, bigger plants when I transplanted them into the garden and exposed them to whatever pathogen this is. I’m also seeing some of the other old, familiar symptoms on these ones: including the discolored fruit.
Collapsed ground cherry.
Leaf necrotic spot and marginal chlorosis.
Spotted, mottled fruit, dropped before fully ripe. (Sorry for the picture quality; that’s the best my camera will do.)
Maybe it’s not soilborne. So I got to rethinking the problem. The discolored fruit made me wonder: could it be viral? Could a virus cause wilting? Yes! Tomato Spotted Wilt Virus (TSWV). This virus, which infects a wide range of plants, causes variable symptoms, depending on host—and fruit discoloration, leaf necrotic spots, wilting and fruit drop can be among those symptoms. Many weeds serve as a host for the virus. And what vectors it? Thrips; and this place is lousy with them.
So is TSWV or a similar virus the cause of this mysterious ground cherry decline disease? If so, the only thing I can do is control thrips—which is not easy. Spinosad kills them, but they can build up resistance. So I’m considering routinely treating ground cherries and other nightshades and susceptible plants with an insecticidal fungus such as Beauveria bassiana, with occasional spinosad applications. Perhaps neem oil is another option?
I’m beginning to think that this same pathogen may also be behind some of my other losses in past years—especially of other nightshades, and sweet peppers in particular. Whatever it is, ground cherries are extremely susceptible.
Has anyone had a similar experience with ground cherries or closely related plants such as tomatillos? Any other ideas about what this might be?