Monday, June 22, 2015

Podocarpus Trees Attached by Beetles

The black twigborer (Xylosandrus compactus) is a beetle that attacks over 200 plant species including orchids, citrus, avocados, mango, coffee, eucalyptus, hibiscus and podocarpus. The females tunnel into woody twigs, leaving pin-sized entry holes. Once inside, they excavate galleries and lay eggs.  This excavation causes the damage to the tree. An infestation by one to three females is sufficient to kill the twig or branch. A severe infestation can kill a plant or even large trees. The damage is not caused by feeding, since the beetle larvae feed on a fungus that is introduced by the female beetle.

Typical symptoms of black twigborer are wilted and dead leaves beyond the beetle's entry hole. The dried, brown leaves frequently stay attached to the tree.

                                                    Entry hole

Cultural control
The best control is to maintain a vigorously growing tree. This will help the tree to resist beetle infestations and recover quickly from existing ones. Prune and destroy all beetle-infested plant material.

Monday, June 15, 2015

Corn Seedlings Hit the Ground

Don't think it's smooth sailing just because the corn seed has germinated and is up and growing.  Young seedlings are often found toppled over. There are three possible culprits for this dilemma.

The two most common offenders are birds and rats. Netting will help to exclude the birds and maybe a scarecrow, too.  Rats will come at night and nibble on the succulent seedlings. Bait or trapping is the solution for rats.

There are also some caterpillars like cutworms, that at night will feed on the seedlings, cutting off the stem at ground level. The plant is not consumed but damaged enough to cause the seedling to topple.

Removing old crop residue and surrounding weeds will reduce the cutworm population. Worms can be hand-picked from the ground at night. Spraying the seedlings and the ground with Bt (Bacillus thuringiensis), an organic pesticide,  may also help.

Photos: University of Minnesota Extension

Monday, June 8, 2015

Planting Trees At the Right Level

When planting trees, never plant them so high that the upper roots are exposed and susceptible to drying. On the other hand, never bury the trunk by planting too deeply; this can predispose the tree to disease. Some trees like citrus are quite susceptible to trunk or crown rot, while some species of trees are somewhat tolerant. Assuming the tree has originally been planted correctly in the container, maintain this same level.

Although a tree may be planted at the proper soil level,  it may later sink due to settling of the soil. What happens is an overzealous gardener will dig the planting hole deeper than the height of the container. The loosened soil that is put back can eventually settle, drawing the trunk down below the soil level. Essentially the planting hole should be as deep as required to accommodate the plant. The sides of the hole may be larger than the original container.  

When trees are near a sprinkler system, remember that the irrigation water should never be directed to hit the trunk of the tree. Again, some trees like citrus are quit susceptible to fungal diseases that occur when the trunk is wet, while other tree species may tolerate this condition.

Trees planted today may last a lifetime. Take the time to do it correctly!

Photo: Monkeypod tree, also known as Rain Tree (Samanea saman)