Plant Virus Diseases

In figure 1 you can see tomato plants that look a bit squirrely. I thought it was possibly herbicide or virus or nutrient problems. After eliminating the first and third we had the plants tested for a battery of viruses. There were 3 viruses found in the plants. The most unusual one was the Pepino mosaic virus, which belongs to the Potexviruses. This virus is very easily transmitted mechanically and has a low seed transmission rate. Seed transmission occurs at rates of less than one in a thousand when seed is not properly cleaned. The virus is external, contaminating the seed coat and not the embryo or endosperm.

Over the years high tunnel (HT) production of vegetables have enabled growers to extend their vegetable production time by 3-5 months. Producing earlier and later season vegetables compared with field production. Though at times it seems HT vegetables have fewer insect problems this is not true and certain pests need to be watched for and anticipated.

I am seeing and getting reports of virus infected squash, pumpkin and cucumber fields, so I thought I’d go over some information about viruses. Several aphid species are responsible for transmission of the most common virusesin cucurbits. Although some cucumber beetles have been shown to vector some viruses (such as Cucumber mosaic virus) their success rate under field conditions makes them a minor contributor to most virus infection problems.

Last week I was in a pumpkin field that had foliar symptoms of a Potyvirus (Fig. 1), but also had some other strange foliar symptoms (Fig. 2). Foliar samples were sent off to Agdia, Inc. (Elkhart, IN) for virus testing. All samples tested positive for a potyvirus (most likely watermelon mosaic virus), while one field tested positive for a virus called Melon necrotic spot virus (MNSV). MNSV is in a family of viruses called carmoviruses, which have been reported worldwide, primarily in hydroponic and greenhouse cucurbit production.

What will be discussed 1.Field problems of early season virus infections 2.Aphid and beetle studies 3.Aphid transmission of viruses 4.Beetle transmission of viruses 5.Recommendations

A couple of high tunnels and even a field of tomatoes have been found with tomato spotted wilt virus in Maryland. The high tunnel finds were not too suprising but the field was a bit as we usually do not see field infections until later in the season.

Garlic growers may be noticing symptoms of virus infection in their plants that show yellowing tips on many leaves with some that are completely yellow (fig 1). If you look closely at the yellow leaves you will see mottling or striping on the leaves (fig 2). These symptoms are usually more pronounced on young leaves. Infected plants are stunted and bulb size can be reduced. Garlic crops infected with viruses are usually more susceptible to weather conditions like extreme heat, and do not keep well post-harvest.

In the last week or so high tunnel tomato plants have been reported that look a bit squirrely. I thought it was possibly herbicide or virus or nutrient problems. After eliminating the first and third possibilities we had the plants tested for a battery of vi-ruses. There were 3 viruses found.

Cucumber mosaic virus in Spinach crops.

The recent discovery of Tomato Spotted Wilt Virus (TSWV) in a resistant tomato cultivar has raised concerns about the emergence of resistance-breaking variants. It is important for growers to closely monitor the situation while continuing to use resistant cultivars.