Thursday, July 24, 2014

Dogwood borers on young pecan trees

   Last weekend I was unwrapping bark grafts and I discovered a graft union covered by  a pile of nasty insect frass (photo at right). Looking closely at the grains of insect excrement, I found they were held together by fine silken threads. I pulled out my pocket knife to scrape off  all the debris when I discovered a cream-colored larvae with a red head.
    The larvae was a dogwood borer (Synanthedon scitula). This larvae definitely didn't like being out in the sunshine and immediately attempted to burrow down under the remaining frass piles (photo at left). Cleaning off all the frass, squashing the larva, and painting the graft union probably saved this graft union from being girdled by the dogwood borer.
    Once I found a dogwood borer in one of my grafts, I started to look at other trees for sign of borer activity. Dogwood borers feed on the inner bark and cambium of numerous hardwood trees and can become a serious pest in young pecan orchards. Adults are clear-winged moths that lay eggs on the bark of susceptible tree species. After hatching, young larvae search for a tree wound, branch attachment crevice, or graft union to enter the tree and star feeding on nutrient rich inner bark. The red arrow in the photo at right points to a column of reddish-brown frass pushed out of a dogwood borer's feeding gallery deep inside a branch attachment crevice. The frass pile usually takes on a tubular shape and is held together by fine, silken strands.

    I also found evidence of dogwood borer infestation on the trunks of young trees. the yellow arrows in the photo at left point to tree wounds created by dogwood borer activity. Piles of reddish-brown frass have pushed out of active borer sites while old borer wounds seem to ooze tree sap (dark black staining on bark).
   Dogwood borers seem to more of a problem in young, non-bearing orchards. Problems with this insect seem to disappear when trees begin nut production and a regular insecticide program is adopted to control nut feeding pest. Insecticides aimed at pecan nut casebearer and pecan weevil will serve to control both dogwood borer adults and emerging larvae.
   Because I found extensive dogwood borer damage all across my young orchard, I will be applying a trunk spray of chlorpyrifos (Lorsban) to knock back the existing borer population. However, if I had been paying closer attention and recognized the borer threat earlier, an early May trunk spray would have been most effective.

Monday, July 21, 2014

Mid-summer maintenance of a top-worked tree

     I've had some outstanding growth on my new grafts this summer and it was time for a little mid-summer tree maintenance. In the photo at right, you can see that the scion has outgrown the bamboo bird-perch that I attached during the grafting process. From this distance, it looks like the new graft is developing into a strong central-leader tree but a closer look reveals the need for some additional summer pruning.
    Even though I trimmed off all the stump sprouts back in June, new sprouts have appeared (photo at left). It is amazing to see green shoots literally pop out of the side of the trunk in such a short time. But like I did back in June, I cut off all new trunk sprouts using my pruning shears.
    Next I inspected the top of the scion.Wow, look at all those stalked buds growing at each leaf axil. If I allow shoots to develop from all these stalked buds, I'll end up with a bushy topped tree and no central leader. It a good thing I brought along a step ladder because I needed it to reach the top of the tree and carefully prune out all these unwanted shoots.
    With all my summer pruning efforts focused on pushing the tree to develop a dominate central leader, I knew it was time to replace the bamboo bird-perch with a more substantial tree-training stake (photo at left). I made my stakes by ripping a 10-foot-long 2 x 4 into 4 stakes measuring 3/4 inch by 1.5 inch (remember a 2 x 4 has the actual dimensions of 1.5 X 3.5 inches).  I attached the stake to the tree using electrical tape (duct tape would also work). I then tied the scion to the stake using 8 mil thick green plastic tape (1 inch wide).
    Judging from the rate of growth I'm seeing so far, this graft union should be completely grown over by the end of next summer (2015). The stake I attached this summer should serve to protect the scion from wind breakage until that time.
   While removing the bamboo bird-perch, I also removed the plastic bag and foil covering the graft union (photo at right). In the past, I've had problems with insects  tunneling in the wood under the wraps and slowing the healing process.
    When I removed the wraps, the bark was almost dripping with moisture. All that moisture can accelerate wood decay at the stock's cut surface so I decided to let the graft union dry out. However, the sudden exposure of the graft union to full sun can cause a sunburn that damages the tree's cambium.  To protect the graft union, I'll use white latex house paint as a sun block.
    I allowed the graft union to dry off while I attached the new tree stake and pruned the central leader (described above). Next, I grabbed a paint brush and painted the graft union (photo at left). Don't be afraid to slap it on thick. Remember the paint's role is to block out the sun and reflect the heat.

Use water-based latex paint only!!  I use exterior flat white.

     When I paint a graft union, I make sure to cover the entire area the was once covered by foil and plastic. This includes the top the stock and the lower portion of the scion (photo at right). The white paint also serves as a visual reminder of which trees have been grafted and the location of the graft union.

   If you would like to go back in time to see how I've top-worked and trained this tree, check out these posts;

1. Changing pecan cultivars by top-working

2. Forcing a bark graft

Monday, July 14, 2014

Identifying nut drop caused by hickory shuckworm

   Most growers recognize the hickory shuckworm as a late season pest that tunnels inside pecan shucks late in the growing season. However, an earlier generation flies in early July and lays eggs on young nuts. In the photo above, the red arrows point to oviposition scars created by female shuckworm moths to deposit eggs in the shuck.
    Once she lays eggs inside the shuck, she scrapes some scales off her abdomen and places them over the hole in an effort to disguise the eggs from predators and parasites. The white halos around each scar are the scales left behind by the female moth.
    At this time of year, it takes about three days after a nut is punctured for that nut to fall from the tree. Fortunately, the generation of hickory shuckworm that causes this kind of nut drop is usually quite small and does not cause enough damage to warrant insecticide treatments.

Friday, July 11, 2014

Planthoppers on pecan

    While trimming my grafts,  I came across a patch of white cottony material on the stem of one of my young trees (photo at right). After looking more closely, I could see a small colony of nymphs hiding within the patch of white fluff. I also spotted a stream of small ants tending the white nymphs.
   The nymphs in the photo are the immature form of the flatid planthopper (Anormenis septentrionalis). Adult planthoppers are wedge-shaped insects that spring off the stems of trees when disturbed. Nymphs are wingless and remain clustered in a group until they reach maturity. Both nymphs and adults are sap feeders, piercing the bark of young trees to feed.
   The ants in the photo are tending the planthopper nymphs. They collect the sugar-rich honeydew secreted by the planthoppers while protecting the nymphs from predators and parasites.
   Planthopper feeding does not pose a serious threat to young pecan trees. Although a large white patch on the stem of a young tree may look bad, an insecticide treatment is not necessary.