Last year, Dr. Zvezdana Pesic-VanEsbroeck (I just call her Dr. Z), who is the director of the Micropropagation Unit at NCSU, came to the county to assess the presence of virus diseases on blackberries. We found virus in every one of our fields to some extent. Below I have posted some pictures of virus disease symptoms on blackberry.
There are many viruses that affect blackberries, some haven't been identified and described yet. Virologists are unsure how some of these viruses are transmitted to blackberries.
We do know that some of these viruses are spread by plant parasitic nematodes, microscopic worms that feed on plant roots. As a result, it is important to take soil samples prior to planting in order to determine levels of plant parasitic nematodes.
We are specifically concerned with a nematode known as Xiphenema, the dagger nematode. Xiphenema is known to transmit the nepoviruses, tomato ringspot virus, tobacco ringspot virus and grapevine fan leaf virus (a devastating disease in vineyards). Xipehema is also known to be a problem in newly planted apple orchards.
Last year a blackberry grower in Henderson County noticed mottled leaves and mishapen berries. Concerned that it might be a virus, he sent it to four different labs across the U.S. Each test came back with the same result, tobacco ringspot virus.
Concerned with dramatically reduced yields and unmarketable berries, the grower has decided to either replant the field in blackberries or to chose a different crop. The first thing we need to do to decide if blackberries should be replanted in the field was to determine the nematode levels in the soil. This is also an important step to help us determine if the virus developed in the field or came in with the plants.
So, I got my nematode/soil samling supplies together. A clean bucket, soil probe, nematode sample boxes from the NCDA&CS, quart plastic bags, a permanent marker, pen and notebook (not shown).
In taking the nematode samples, I made sure to sample both the healthy field and the problem field. I took samples from the healthy field first, making sure not to contaminate it with soil or nematodes from the problem field.
I took 20-25 soil and root cores from the beds. The samples were taken from 8-10 inches. Because Xiphenema is usually found in the root zone soil (they are migratory ectoparasites, meaning they move from root to root piercing them to feed), I took the samples as close to the plant and drip-line as possible. This required some major work getting into that dense plant canopy. I took samples throughout the planting, making sure to get a representative collection.
Next, I took 20-25 cores from the problem field. Again taking samples close to the plant and drip-line. For this site, I made sure to take the samples from symptomatic plants.
I am anticipating the results from the nematode test. If it comes back with levels of Xiphenema that are high, the grower has a few options.
- Plant a different crop in this site for a few years (Xiphenema reproduces once per year and can live four to five years) before replanting in blackberries. Brassica crops are a good option. They are known to have some properties that may decrease the levels of plant parasitic nematodes.
- Plant this site in a new crop entirely. Xiphenema has a wide host range, which includes perennial orchards, grapes, strawberries, grasses, forest trees (spruce, pine) and even some weeds. I am having a hard time finding crops it doesn't do damage.
- Use a fumigant to treat the land prior to planting. Fumigants labeled for blackberry nematode control are metam sodium and telone. These need special equipment for application and may have an 8 week pre-plant interval. Refer to the NC Ag Chem Manual for more details.
For more details on nematode sampling, visit the NCDA&CS site.
Your local Cooperative Extension office can provide the test boxes and assistance.