July "In The Grow" - Indiana Yard and Garden - Purdue Consumer Horticulture

July “In The Grow”

Q. We have a big problem with bagworms. Last year they destroyed two decorative pine trees in our landscaping and they love our plum trees also. I cannot begin to count how many of their cocoons are left in our landscaping. What can I put on my trees and other plants to keep them from making their home too close to mine? Also, what time of the year should I take care of this problem?- Karen, Ferdinand, Ind.

A. I share your misery! I have bagworms on a large planting of arborvitae. In the past, it’s been a small enough problem that I handpicked some of the bags (a preferred method for

small infestations) but obviously I missed some and now the problem has grown. The caterpillars that live inside, construct spindle-shaped bags to protect themselves. Since they’re composed of bits of foliage, they blend in with the tree incredibly well until extensive damage is noticed or the brown bags, resembling pine cones, are seen much later in the year.

Bagworms can be controlled chemically by spraying infested trees in early summer when the eggs hatch and young worms appear. Bacillus thuringiensis is the preferred insecticide because it selectively kills bagworms and not the natural enemies of other pests. Other insecticides labeled for bagworm include malathion, carbaryl (Sevin) or a pyrethroid like Eight.

Bagworms usually emerge in early to mid-June. Apply insecticides when bags are between 1/2 inch and 1 inch long. Each bag has about 1000 eggs and it can take several weeks for all of them to hatch so check two weeks after spraying to look for new live bags to determine if additional treatment is needed.

For some great photos of bagworms in different life stages, go tohttp://www.entm.purdue.edu/entomology/research/cs/notes/307E/lab7/7.3.html

Q. In one of your recent columns you mentioned a good shade- loving vine. I lost the copy and wondered if you would again mention the name of that vine in this letter. I would appreciate that. – Jan Van Dokkenburg

A. Virginia creeper, Boston ivy, and English ivy are all shade tolerant vines. My favorite shade tolerant vine is climbing hydrangea. It slowly becomes established, then takes off with green foliage and white flowers. Other choices include silver lace vine and vining honeysuckle cultivars like ‘Dropmore Scarlet, but keep your eye on these choices. They can cover more ground than you originally intended.

Q. I have a flowering, large round leafed plant in my yard. I call it a wild violet, for lack of a better word. It is invasive, and nothing seems to eradicate it except “Round Up ” (glyphosate) and digging it out. Is there any other chemical I can use to eradicate it and not harm the grass? -Bill Fleming

A. If you have violets, they are tough weeds to control. Mid- September to mid-October is the best time to apply a herbicide. This is when the weeds store energy reserves for the winter in their roots so the herbicide will be translocated to the roots and give a greater degree of control. Don’t expect it to eradicate the violets completely, but rather to reduce the population.

If the violets are growing in turf, they tend to grow in shady areas where the lawn does not compete as well. If you can prune back trees or otherwise get more sunlight there, the turf will be invigorated and better able to hold its own ground.

For more information, call your county Extension office and ask for Control of Broadleaf Weeds in Home Lawns (AY-9) or find it online at http://www.agry.purdue.edu/turf/pubs/ay9.htm. Proper identification of the weed is desirable so you can plan the right attack. Bring a sample to your county Extension office.

Q. I have two rhododendron bushes in my garden. A few weeks ago, one of them developed spots resembling rust on the leaves. The affected bush continues to have new growth, but I am worried that it may have some type of blight or fungus. I would appreciate any suggestions on how to treat this problem. – Karen Munson

A. Several different fungi cause rust on rhododendrons. Yellow spots, up to 1/4 inch in diameter appear on the upper surface of the leaf. Underneath the leaf, are spots or blisters containing yellow or orange spores that are spread by wind. No chemical control is available but you can pick off infected leaves to reduce the spread of the fungus.

Q. I want to know about rolls of black paper that allow moisture to penetrate. How long will it last? How well does it work with tomatoes and keeping out weeds?- S. Campbell,, Bloomfield, Ind.

A. The black landscape material used most often is a fabric, not paper. Its useful life depends upon conditions. Put the fabric down on the ground a few weeks before your frost free date and allow it to help warm the soil. Then cut holes for the tomato transplants. At this point, I usually put a mulch over the top of the fabric. Mulch helps retain moisture and keeps the soil cooler during the heat of summer. Over the years, it’s possible for weeds to germinate on top of the fabric in the accumulated decomposed mulch but this causes far fewer weeds than if you had not used a barrier for weeds at all.

There is a black paper mulch on the market. It is more water and air permeable than plastic, but not as much as fabric. The plain black paper tends to degrade where it is buried along the edge fairly quickly (less than 2 months) and you could not put an organic mulch on the top to reduce summer soil temperatures without causing the paper to decompose. Some paper mulches are treated with wax to slow degradation, but these would then not be water permeable. The biggest advantage to paper mulch is that it can be tilled in so disposal is a breeze.


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