JULY
2006

 

 

 

By
B. Rosie Lerner
 
Purdue
Extension
Consumer Horticulturist

 

 

 

 

 

07-06-06

Question and Answer

Q. My husband pulled out a weed in the garden that made his hands burn for quite a while. It had sharply serrated leaves that were opposite. The stem looks almost square and ropey, with fine hairs along the whole length. Do you have any idea what it is?

A. Stinging nettle is most likely the culprit, with its stinging hairs along the stems and on the undersides of the leaves. These perennial plants grow 2-7 feet tall and have opposite leaves with saw-toothed edges. The plants have greenish, non-showy flowers. According to the Purdue Veterinary School's Web site on poisonous plants http://www.vet.purdue.edu/depts/addl/toxic/plant31.htm, the small, hollow hairs in stinging nettle contain several irritating substances, such as histamine, serotonin, acetylcholine and formic acid. These substances, coupled with the hairs' ability to scratch the skin and mucus membranes, result in almost immediate burning, itching and irritation. The irritation usually resolves on its own.

Q. I have these stickery weeds growing in part of my yard. They are spreading to more of my garden and part of my backyard by the garden. They have a long white root. I've tried pulling them out, but they seem to keep spreading. I'm afraid to spray them in my garden because of the food. Can you tell me what to do to get rid of them?

A. Herbicides that would kill broadleaved weeds would also be likely to damage the vegetables you are trying to grow. There are a few pre-emergence herbicides (such as those that contain trifluralin) that can be applied to garden soil around some (but not all) vegetable crops, but these are aimed at preventing new weeds from germinating from seed. To control existing weeds, hand-pulling and shallow hoeing or tilling around the veggies are your safest methods of weed control. Mulches will help discourage new weed growth. The Purdue Extension office in your county can help you identify the specific weed, if you bring them a sample, and perhaps be able to make more specific control recommendations.

Q. I am looking for information regarding a product to prevent the sweet gum trees from producing their gumballs. This spring, I was told that there is now a product, but so far, I have found nothing on the Internet. These gum balls are a big problem for me. I live on one-and-a-half acres and have at least 25 gum trees.

A. I'm afraid there really isn't a practical solution for completely preventing fruit on large, well-established trees, but there are some hormone-based products that can help reduce fruit set. One such product is ethephon, sold as Florel Brand Fruit Eliminator®. It must be applied at just the right dosage, at just the right stage of flowering (full bloom) and at just the right temperature range. There is risk of plant damage if dosage and/or temperature are too high. In fact, plant stress of any kind can increase the likelihood of plant damage. And, because the product must be sprayed on, the effectiveness will depend on being able to get complete coverage of the canopy, not an easy task on a large, mature tree.

There is another product called Snipper® that is designed to be injected into the tree while the flowers are still in bud stage. However, the application uses a micro-injection system that requires skilled precision. Like other hormone treatments, timing and dosage are critical. This product should only be applied by a professional.

You might want to contact a certified arborist for estimates on both of these methods. The price of fruit prevention might make sweet gum fruit cleanup a bit easier to accept!

Q. Something is eating my irises. Whatever it is, it's taking the stalks and the unopened buds. They seem to do it at night. Can you help? And what do we do about it?

A. Grasshoppers and cutworms both feed on many species of flowers, but cutworms are notorious for doing their work at night and usually hide in the soil, or under mulch and leaf litter, during the day. If the population hasn't gotten too large, you might be able to solve the problem by handpicking the larvae from soil and mulch. Morning is the best time to look for them. Cleaning up leaf litter and pulling mulch away from the plants will also help remove their hiding places.

If damage is severe enough to warrant insecticide use, you can try using a dust formulation of carbaryl around the base of the plant. Do not apply the dust to the flowers as carbaryl is highly toxic to bees.

Q. For the last several years, we have had problems with some sort of blight in our tomato crop. The bottom half is blackened and flat. The top half is good to eat. Not all of the tomatoes on the plant will be affected. Sometimes, as the summer goes along, it gets better. But, overall, as the years go by, the problem seems to be getting worse. We have changed and rotated the place where we plant, and have changed fertilizers and types of plants. Any suggestions? We have a large garden each year and can everything, so I need a good tomato crop.

A. You have just perfectly described a very common disorder of tomatoes called blossom-end rot. The black scar tissue is caused by a deficiency of calcium in the developing fruit, usually brought on by extreme fluctuations in soil moisture. The spot develops on the blossom end of the fruit, thus the name blossom-end rot. The scar is usually firm and leathery, although secondary rotting organisms may enter through the damaged tissue and cause a soft rot to develop.

Tomatoes aren't the only fruits affected by blossom-end rot; summer squash and other cucurbit-type plants are less-often affected.

Once the fruit has already developed the scar, it can't be cured. However, you can try to prevent blossom-end rot before it gets started. Watering during dry spells and mulching to conserve soil moisture will help reduce fluctuations in the moisture supply, preventing calcium deficiency in the fruits.

 

Writer: B. Rosie Lerner
Editor: Olivia Maddox,