QuestionQUESTION: The last five years the leaves on our back neighbors quaking aspen have been falling on our garden......I feel because of this we are fighting disease on our tomato, cucumber and bean plants. We have never had that problem before. I try to pick up what I can, but they drop every day. This year my husband cut off all the branches that hang over our garden to see if that helps, but it hasn't. He tills in the fall. We are organic gardeners and I have used organic sprays, but still have the problem. Is there anything we can do to sterilize the soil this winter.....or is this just a lost cause until the neighbors get rid of the trees. We don't want to be bad neighbors and cause problems with them, but this is a huge problem. Our tomatoes leaves are turning yellow from the bottom up, then dying. Our plants grow tall and are producing some tomatoes, but not a lot. They are all heirloom plants. They are our worst problem. Bean plants are diseased also...and a little on the cucumber plants with white spots. I am vigilant at removing diseased leaves and stems. Hopefully, you have a solution. Thank you.
ANSWER: The leaves from your aspen are not the cause of the problem in the garden. The pathogens that would attack aspen are not the same organisms that would attack your garden plants. Plant pathogens are relatively restricted in host range so something that would attack tree leaves is not likely to attack your garden plants.
It is more likely that the problem is caused by something in the environment or another problem that is unrelated to the tree. I am assuming that the garden gets full sun and that the tree would not be blocking light. Vegetable plants need full sun to perform well and if they are shaded, they will not be very healthy.
The problem with your tomatoes may be related to fertility or temperature issues. Have you had the soil tested to determine pH and nitrogen, phosphorus and potassium (N-P-K) levels? Soils in your area often have a higher pH which is not the best soil for gardening. There are amendments that can help reduce the pH and may help with the problem. The soil test can probably be done through your local county extension office. Contact them about sampling procedures and where to take a sample. There usually is a charge, but it is to cover the cost of the tests done by the lab. In my state, they charge $10 per soil sample for pH and N-P-K. You can find your local office at this website: http://extension.usu.edu/htm/counties/. They will be able to give you the details for your area. The extension educator may also have additional fact sheets or information on gardening in your area which could be useful.
The reason I recommend the soil test is because if the plants are receiving too much or too little fertilizer or have improper pH, your yield will be reduced. Heirloom plants in general have lower yields that newer varieties. If they have too much nitrogen, the plant will put on vigorous leaf growth and not have many flowers or fruits. I am not sure of your summer temperatures, but if the temperatures are consistently over 90F the yield will be low. Tomatoes do not flower as well and do not usually set fruit when temperatures are above 90-95F.
As for the yellowing on the lower portion of the tomatoes, it is possible that the problem is due to spider mites or to Septoria leaf spot. Spider mites are a problem in mid to late summer on tomatoes and you can usually see evidence of them on the underside of yellow or brown leaves. The green leaves may show stippling or silvering where the mites are invading. If you see webbing or "dirt" on the underside of the leaves then you may have spider mites. They are difficult to treat organically and usually show up late in the season when the tomatoes are mostly done. You may be able to use a horticultural oil product or insecticidal soap, but it will most likely require more than one treatment.
If it is Septoria leaf spot, I would expect that on some of the leaves that are yellowing, you would see circular brown spots. There may be many circles and they will coalesce so larger areas turn brown. Organic options include fungicides containing copper or potassium bicarbonate. You will want to be sure to remove the plants and fallen leaves at the end of the season and discard them in the trash. Do not compost these leaves because you may not reach high enough sustained temperatures to kill the pathogen spores.
As for the beans, I'm not sure what the disease problem is based on the description. I am not sure if the white spots were only refering to the cucumber or also beans. If it is white spots on the leaves, it may be powdery mildew (see below). Otherwise, beans are a cool to warm weather plant. They should be planted just after the last frost and are usually done 50-65 days after planting. They are another plant that does not like hot temperatures and will not flower well or set pods when the temperatures go up.
You indicated that the cucumber has white spots. This may be powdery mildew. This disease is common on cucurbits and usually shows up in the summer when it is warm and dry, but still humid. There may not be that much humidity in the air, but close to the soil where you are irrigating there will be humidity. There are organic sprays that you can use for powdery mildew. You can use sulfur or potassium bicarbonate which can be purchased at a garden supply store or a homemade baking soda spray (similar to the potassium bicarbonate product that can be purchased). I have not used the baking soda spray myself, but have heard that it does provide some control. There are many recipes on the internet for baking soda sprays and you can pick one based on what you have in your kitchen. Be sure to test the homemade spray on a few leaves and wait a few days before treating the entire planting. Some plants are sensitive to the components that may be in the recipe (oil, dish soap) and you want to verify that your plants can tolerate it. If they cannot, the leaves will burn up (phytotoxicity) and die.
I hope that this answered some of your questions. If you need additional questions, please let me know. Good luck!
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QUESTION: Thank you so much for your response. We will be sure to have our soil tested. I know the problem is not spider mites or Septoria Leaf Spot, More likely Fuserium wilt or Verticillium wilt or something like that. And I know that is a soilborn disease that can stay in the soil for years. We have gardened for over 40 years and haven't had these problems before this last five years. I used insecticidal soap early in the season because we had a huge aphid problem in Salt Lake because of a long, cold, wet spring and we had aphids for the first time, but I think I got on top of that and we have used the organic products you mentioned. But every day I have to cut off dying leaves as the disease is climbing up the tomato plants from the bottom. I think the cucumbers are doing fine now except for some white spots on the leaves, but they are producing sweet cucumbers like crazy. Our onions are gigantic, squash, and peppers are doing great, but I can't seem to get on top of the problem with tomatoes. The only thing we are using different this year is Spray-n-Grow and I have been following their directions. I am considering getting Neem Oil and see if that works. I looked on the Ohio State U. website and saw there recommendation to cover the soil with clear plastic for six weeks and that would kill whatever is going on in the soil. We would have to do it next June through July 15 when the weather is hot enough and that would mean planting very late. Our garden gets full sun and we have lots of organic matter and compost in it that we till in each fall, and we throw away anything that is diseased when we clean up in the fall. I just wish we could get rid of this problem. Do you agree that we would have to cover it in plastic if this is a soilborn disease? Thanks for any additional light you could shed.
AnswerThe symptoms of Verticillium and Fusarium wilt are pretty clear if the disease is severe. If you cut into the larger branches or main stem, a healthy plant is green and white inside. If it is Fusarium or Verticillium, you will see rusty brown streaking inside the stems. You may have to sacrifice a plant because the main stem is often the most diagnostic. This website has a good picture of the streaking:
http://ohioline.osu.edu/hyg-fact/3000/3122.html
Be sure to examine a plant that is declining (wilting, yellowing), but not dead. In a plant that is very close to death, the internal tissues will naturally turn brown and can be misleading.
If you think you have one of these diseases, you may want to select disease resistant plants for next year. Even with heirloom tomatoes, as long as your varieties are named, you can often find information about whether or not the varieties are resistant to Verticillium and Fusarium on the internet. You may see V for Verticillium resistance and F, F1, or F2 for Fusarium. F and F1 mean it is resistant to race 1 and F2 means it is resistant to race 2.
As for using plastic, the process is called solarization. Two of my colleagues wrote the fact sheet that can be found at the following website:
http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2649/EPP-7640web.pdf
It gives the basics of solarization and it certainly is helpful. Be sure to shovel or plow the soil because it loosens the soil and allows better heat penetration. Although it is best to do it in the late summer, there is certainly good value in doing it in the winter months. You may need to leave the plastic on longer or may have to reapply the plastic if it is damaged by winter storms. You could try solarization on the whole garden in the winter and then during the more favorable time, just do half the garden. That would allow you to plant the other half at the normal time. Most soil-borne diseases are not airborne and are only moved by soil and water movement. So, if you can control the direction of drainage, this may be a way to do solarization over two summers rather than impacting your entire garden at once. You could also test how well it works. Adding organic matter is also very helpful in reducing soil-borne diseases. Studies have shown that using compost is one way to help reduce diseases.
Good luck!
