Oak leaf blister

Question: Why would oak leaves start falling off the tree in the late spring or early summer?

Answer: Check the leaves closely for small spots that are often cup shaped. Some of these spots appear grayish while others are green, but all are characterized by small puckered areas. If this is what you are seeing it is likely a fungal disease called oak leaf blister. This particular disease affects many species of oaks and is a problem whenever our spring is wet and cool late into the season. Although it has been hot over the last month think back to early spring and you may recall we had a cool wet spring (in the mid-south US). Although infection took place much earlier you may only now be seeing leaf drop. On the plus side even heavy infestations are not a cause for concern.

Some of the infected leaves will not fall from the tree until the normal leaf drop period in early fall. When conditions are right and infected old leaves are preparing to drop for the winter, they will produce spores that infect the developing buds that will form the new spring leaves next year. This is the way the cycle repeats itself each year. If weather conditions are not right for infection next year you may not even see the disease. Again, the disease does not pose a serious threat to tree health so there is no need to spray with a pesticide. For information on other possible oak tree pest click here.

Mystery Muscadine

Last week I had what I thought was an easy question that forced me to dig deeper than I normally would have. A lady called with a question about her muscadine plant that she relocated to an arbor three years ago and she has never gotten any fruit off of it. I assumed she had a female flower type and no perfect flowered variety nearby. Typically you will find nurseries selling varieties that are either female or perfect flowered types. If you plant a female type alone you will not have fruit but many of the female varieties have desirable fruit. Therefore, they are planted with perfect flowered forms nearby to provide pollination.

This lady really wanted to know for sure so I asked her to bring a bloom sample in to get a closer look. After looking at the sample it was apparent she did not have a female variety as I originally assumed but a male plant that is totally incapable of fruiting (see photo above). Male plants are not uncommon in the wild but what really confused me was she said the plant was dug from an abandoned vineyard on her property. Why would anyone plant a male plant I wondered when a perfect flowered plant would produce pollen and fruit? When she told me the vineyard (she believed) had been planted in the 1940's that gave me a critical clue.

I pulled out an old textbook from my college days and found out that until 1948 there were no perfect flowered varieties available and growers were forced to plant male plants to act as pollinators for the female varieties. This lady had the bad luck of moving a male plant which were usually planted at a 1 to 8 ratio in these old vineyards. Of course in the wild you still find plenty of these male plants but they probably only exist in very old vineyards planted before perfect flowered forms became available.

Tomato Problems

Question: This year I decided to grow my own heirloom tomatoes because they are so expensive in the store but the lower leaves are dying and the problem is moving up the plant. Can you tell me what is going on and how can I stop the plant from dying? Also, I have heard a lot about tomatoes and salmonella lately – should I be concerned about my garden tomatoes?

Answer: Now you know why heirloom tomatoes are so expensive. Most of them have little or no disease resistance and they tend to make a lot of foliage compared to the amount of fruit produced. This is another reason for their expense plus a possible reason for increased disease. The large amount of foliage means the foliage stays wet longer after rain and dew. Wet foliage means increased foliar diseases like “early blight” which is the likely culprit on your plants. The relatively cool wet weather earlier this spring made for perfect conditions to spread early blight. Click here for other disease possibilites: http://www.aces.edu/pubs/docs/A/ANR-0895/

Early blight is the most common and widespread foliar disease on tomatoes in the southeast. If not controlled, this disease can severely damage fruit quality and lower yields. On young plants, dark brown, irregular spots form and completely encircle the stem, causing plants to quickly wither and die. On older plants like yours, the spots are restricted to one side of the stem. Leaf spots, which typically occur first on older leaves, begin as small (1/l6 to 1/8 inch in diameter), dark, irregular spots and enlarge to form larger spots up to ½ inch in diameter. Tissue surrounding these spots often will turn yellow, resulting in early defoliation. On severely infected plants, fruit may become sunscalded because of the lack of foliage for protection.
Once the disease becomes severe on individual plants control is unlikely. Removing infected leaves from the garden can help. Other cultural controls for this disease include; mulch to prevent soil splashing onto lower leaves, proper fertilization, don’t wet the foliage when watering, stake or cage the plants and prune off side shoots. Fungicides are also available and do a good job preventing disease but they don’t cure disease.
Let me elaborate on a couple of the cultural control options. Nitrogen fertilizer is a good thing for plants like tomatoes that grow fast but excessive fertility leads to growth that is often more susceptible to pest. There is a fine line between enough and too much fertilizer. If your plants are dark green and growing very fast you may have crossed the line. Along a related path you might want to prune excess growth off by removing side shoots called suckers. These suckers grow from the main shoot at an angle from leaf attachment points. In general they are less fruitful and the thick growth that results is more prone to disease because it is vigorous and causes the plant to dry slower after a rain or dew.
I have a couple thoughts about your salmonella question. First, salmonella is not a disease that tomatoes can contract but a contamination that can happen during harvest and/or packing. Second, it is possible to have salmonella contaminate even your garden tomatoes. As a precaution you should never apply fresh animal manure to the soil surface when vegetables are in the garden. Always compost animal manures well or till them into the soil before planting. Consider using a mulch around plants to reduce the risk of animal fecal matter splashing onto tomato fruit and other vegetables. Tomatoes that are home grown or vine ripened locally are very unlikely to pose a serious health risk. Nevertheless, even your own garden vegetables should be handled with clean hands and washed thoroughly before eating. You should take the same precautions you expect your favorite restaurants chef to take when handling vegetables to be eaten raw.