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Leaf Spots

(November 2010)

QuestionI live out on the north side of a small mountain in the Ferndale area.  I try to grow things on our ten acres, with modest success. I set out blackberries a couple of years ago, beside a small running creek, but not below water level. This summer, they developed some black spots and a couple of vines passed on, the remainder did produce a couple of quarts.  I am thinking they had  some kind of a rust perhaps, because I do have oaks and cedars in our area. Should I be applying some type of dust such as rotenone?


AnswerThere are several things that could be impacting your blackberries, but from the sound of it, it isn’t insects, so rotenone would not be affective.  I also don’t like dusts.  If you are going to spray, we need to properly identify the disease (with leaf samples next year) and then find the appropriate fungicide.  There is one disease called double blossom (or rosette) that affects blackberries that is not curable. It is common when we have wild blackberries nearby that can spread the disease.  It causes excessive thorniness on the stems and deformed almost double blossoms—thus the common name.  It can kill plants, but usually in a slow manner.  Pruning out infected canes helps.  There is a rust disease that affects blackberries that is controllable. It produces very bright orange spores that can be rubbed off.  Cedar apple rust does not affect blackberries, but does affect apples.  There are other leaf spotting diseases as well as stink bug damage to the fruits.  If you have the problems again next growing season, bring in a sample or take a picture and send it in so we can properly identify the problem before recommending a control.

QuestionWe have been having problems with our "Sweet Ones" tomatoes since early summer.  The leaves are covered in tiny spots. We sprayed with Sevin several times to no avail.  We are hoping that you have an answer for us as to what it is and how we can stop it.  This is the first time in all the years that we have planted tomatoes that this has happened.  It seems to start at the bottom of the plant and work its way up to the top of the plant and go from plant to plant.  Thankfully our plants have continued to flower and yield tomatoes up until this week when either the disease and/or the weather got them.


AnswerWhat you have is a disease, not an insect problem, so the Sevin was totally ineffective, since it is an insecticide.  There are several leaf spotting diseases.  The most common is septoria leaf spot, but there are others as well including early and late blight.  Many tomato diseases are soil-borne, so rotating where you plant your tomatoes is important.  There are preventative fungicide sprays for tomato diseases, including Daconil and Bravo.  Make sure you read and follow the label directions for the waiting period between applications and harvest. Many of these diseases hit annually, so I think you are lucky you haven't seen them before.  Often you can harvest enough fruit not to worry about spraying.  Treating once you have the problem is often ineffective, it can slow the disease down, but it doesn’t get rid of it.

(July 2005)

QuestionI have several pots of impatiens and some of the plants have brown spots on the leaves.  A few of the spots have holes in the middle.  Also some of the leaves are turning yellow.  Not all of the pots have this trouble and we can't figure out what the problem is.  Every year our impatiens do this.  The plants grow huge and blossom well but the spots ruin the looks of the plants.  Can you help me?


AnswerThere are several possibilities but the two most common would be Impatiens necrotic spot virus (INSV), (which used to be called Tomato Spotted Wilt Virus on impatiens), or Alternaria leaf spot.  INSV is spread by tiny insects called thrips.   Symptoms can include stunting, brown or yellow circular spots on leaves, ring spots, black or brown stem discoloration, or mosaic patterns (variegated patterns of light and dark green).  There is no cure for this disease, other than sanitation.  Alternaria leaf spot is another possibility. Often, one cultivar is severely infected while other cultivars appear disease free. Look for small (about 1/8 of an inch), round, light tan circular spots surrounded by a purplish border. Severely infected leaves can turn yellow and drop from the plant. Alternaria leaf spot could be confused with spotting from impatiens necrotic spot virus. Avoid prolonged leaf wetness, and if only a few plants are infected, dispose of them.  Daconil can help in control of this disease.  The holes you are seeing in the leaves is probably from dried tissue from the disease.  Make sure you are cleaning your containers well at the end of the season and disposing of the used potting soil.  Start with fresh soil every season, especially if you experienced problems the year before.  If you are uncertain what the problem is, take a good sample to your local county extension office.  The county office can send the plant to the disease diagnostic lab for a proper identification.  Once you know the problem, you will have a better chance in controlling it.

(July 2006)

QuestionI have heavy infestation of my Fraser's Photinia hedge with black spot on the leaves. Not all bushes are infected but those that are, seem to be very heavily spotted. Any quick cure? Can they be saved? Any help would be appreciated.


AnswerUnfortunately, there is no such thing as a quick cure for entomosporium leaf spot of red top photenias.  This leaf spotting disease is quite similar to black spot on roses and would need weekly preventative spray programs for total control--not worth the effort in my opinion.  You can spray two to three times in early spring before the disease kicks in for the season with a fungicide such as Immunox or Daconil, but if they were my bushes, I would start planting a more disease free hedge nearby and gradually replace them.  WE have been losing red tops across the south for twenty years now and they are not worth the effort.


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