QUESTION: I have several cucumber, pumpkin, and squash plants that have discolored and distorted leaves. I see no insect damage and have sprayed for powdery mildew. The plants have adequate nutrition and are watered regularly. What's wrong with my plants?

ANSWER: Your curcurbits (squash and melon family), have been infected with a virus. Plants have mottled leaves, that is patches of green and yellow, often in varying hues mixed in the leaf. Whole plants and leaves are usually smaller than normal and many times deformed and fragmented. Cucumber, melon and squash fruit are also small, stunted and unusually colored. The fruit can even be bumpy and have warts! There are several different viruses that infect this family of plants. They include: cucumber mosaic virus (CVM), squash leaf curl virus (SLCV), squash mosaic virus (SQMV), watermelon mosaic virus (WMV) and zucchini yellow mosaic virus (ZYMV). Each of these pathogens usually have several strains. Sometimes an infected plant may have more than one virus causing the symptoms. Therefore, it makes an exact diagnosis difficult without laboratory analysis.

Viruses cannot survive outside of living organisms. They may be present in seeds when planted. This which occurs with SQMV. Insects serve as vectors, (transmittal agents), for many viruses. Sucking insects like aphids and white flies and chewing insects such as cucumber beetles and grasshoppers transmit virus particles from infected plants to healthy ones.

Control: When virus resistant varieties are available their use is advisable. Control host plants such as related weed species and infected crop plants which serve as reservoirs of viruses. Destroy these plants as soon as symptoms appear. Control insects which transmit viruses. I know of no chemical or natural cures for viruses in plants. In many cases plants will survive in a weakened state much like what happens to humans when we get a viral flu or cold.