SEPTEMBER
2001

 

 

 

By
Beverly Shaw
 
Advanced
Master Gardener
Purdue University

 

 

 

 

 

09-06-01

Question and Answer

Q. I have a weed in my garden that I can't get rid of. It lies close to the ground and spreads. It has small green leaves that are thick and feel like rubber. Is there anything you can tell me to help me get rid of it? Thank you. - Sheila Denton, via e-mail

A. It could be a number of weeds but sounds most like purslane. Purslane thrives in hot, dry weather. The green, rubbery leaves are 1/2-1 1/2 inches long on thick, reddish- green stems. It sometimes bears yellow flowers, and the seeds are borne in a small pod with a top that comes off like a lid on a cookie jar. If this sounds like the weed you have, read on. If not, take a sample to the Purdue Extension office in your county for identification.

Chemically, you can treat with glyphosate (sold as Round-up or Kleen-up) but you must use care. Any green plant material sprayed with glyphosate is killed, so spraying with this non- selective herbicide is not recommended anywhere near desired plants, like vegetables or flowers. If the purslane is growing in your turf, you could use a broadleaf herbicide.

In this case, however, the best method is probably pulling by hand. Since purslane roots wherever it touches the ground, any plants that are pulled or hoed must be completely removed from the garden, or they'll root again! Instead of reducing the population, hoeing can increase it. A layer of mulch at least 3 inches thick will help reduce weed populations from garden beds. Purslane is a warm-season annual, so weed removal, mulch and a pre-emergent herbicide can prevent the same problem from reoccurring next year. If you're directly seeding new vegetables or flowers in the garden, do NOT use a pre-emergent herbicide, as it will keep those plants from germinating.

On the up side, purslane is an excellent crunchy salad plant. Check out http://aggie- horticulture.tamu.edu/plantanswers/98promotions/april/recipes.html for a host of recipes for stems and leaves, including Purslane Con Queso, Pickled Purslane and Ham and Purslane on Rye! Another Web site with loads of information is http://www.hort.purdue.edu/newcrop/1492/neglected.html#Purs lane. Here, you'll find ways to increase production (if you just can't get enough of it) and interesting purslane facts.

Q. For no apparent reason, the leaves on my mountainash are turning yellow, drying and falling off the tree. Is there any treatment for this condition?

A. There are several species of mountainash but all are of the genus Sorbus and all are susceptible to a great number of diseases and insects. Fireblight is common; crown gall, canker, leaf rusts, scab, aphids, pear leaf blister mite, Japanese leafhopper, roundheaded borer, mountainash sawfly and scales and borers all find mountainash to their liking. To accurately diagnose the problem with your tree, you'll need to inspect it more closely. Look for anything unusual on the leaves, branches and trunk and take samples to your Purdue Extension office in your county.

In general, these are not highly recommended landscape plants, due to the potential problems and short life expectancy. This is a shame because the highly colorful fruiting in the fall is spectacular. The best line of defense is a vigorously growing tree given plenty of fertilizer and water during the growing season. The Korean mountainash (Sorbus alnifolia) is least susceptible to borers and has the most aesthetic fruiting effect. This tree should not be planted in stressful situations (for example, as a street tree). It prefers a cool, moist climate that is difficult to replicate in Indiana.

Q. For the first time in 50 years of gardening, I have whiteflies. I have tried everything. My cucumbers and tomato vines all died so I pulled them out. I notice they are spreading to my roses, and I'm fighting to keep them out of my asparagus and rhubarb. Please advise what to do other than never to buy my plants at that nursery again. - Audrey Gilland Fort Wayne, Ind.

A. First, the good news. Whiteflies are basically tropical insects that will be killed off by our cold Indiana winters. Be careful not to overwinter any by bringing infested plants into the house this fall.

The bad news is that they have five stages of development, and each stage has a varying susceptibility to insecticides. Since all life stages can be present at one time, it's impossible to identify the stage and apply the appropriate insecticide. Treat with diazinon, malathion, orthene or insecticidal soap, but make sure you follow the directions concerning reapplication, so you control new whiteflies as they hatch. Most insecticides require at least three applications at intervals of four to six days. Since this is on edible crops, make sure the product is labeled for use on that crop, observe harvest restrictions and read and follow all other label directions.

You can also purchase sticky, yellow traps and hang them in the infested plants. The whiteflies are attracted to the yellow color and once they land, they can't take off again.

Finally, it's unlikely that the whitefly actually is what is killing your plants. Although whiteflies do suck sap out of the plants, their main threat is in the possible transmission of virus, and viruses tend to be more host- specific. With so many different sorts of crops dying, it isn't likely that a virus from the whiteflies is the culprit. Put on your detective hat and search for cultural problems, including watering practices, soil conditions, etc. I would still try to get the whiteflies under control, however.

 

Contact: B. Rosie Lerner
Editor: Olivia Maddox,