Leafcutter bees destructive to some plants, beneficial to others
Q: My recently planted Carolina jasmine vine and rose bush are being shredded by cutter bees. I’ve been told there is no insecticide to kill or deter them. Is this so? Both of these plants are adjacent to other plants but the others are not affected. I’m at wits end seeing perfect circles in the leaves! Also, why would you want cutter bees?
A: Leafcutter bees can be pretty destructive to the appearance of many plants. They are pretty selective in the plants they choose. Other plants affected in addition to Carolina jasmine and roses include bougainvillea, grape leaves, basil and other leafy herbs, photinia and ash leaves.
Part of the female leafcutter bee’s life cycle is to cut circles out of soft, thin, smooth leaves and use them to build nests for their young. The nests are constructed of individual cells, each with a ball of nectar, pollen and one egg.
They build these nests in cracks and crevices and holes that vary from about 1/4 inch to 3/8 inch across and deep enough to construct individual cells for their young. They also build nests in the stems of some pithy ornamentals like roses.
A frequent recommendation among rosarians is to seal pruning cuts in roses with Elmer’s glue, a safeguard against leafcutter bees nesting in rose canes.
Leafcutter bees are important pollinators of commercial crops and were introduced into the United States from Europe. They have been used in Nevada for pollinating alfalfa primarily.
The bee is slightly smaller than a honey bee and won’t sting unless highly provoked or injured. Because they are such prized pollinators of urban vegetable crops, I encourage people to live with the damage they create or drape affected plants with cheesecloth to keep them away.
If you want to reduce their populations, another method to control damage, you can put out bee boxes, which are blocks of wood drilled with holes large enough to accommodate a portion of a soda straw. The females deposit their eggs inside the soda straws. You can dispose of the straws when they are full but before the young bees emerge.
Using insecticides is highly discouraged and it doesn’t prevent the damage anyway.
Q: Over the past two days, my two Concord grapevines have been completely defoliated by a larva-like worm. It is yellow in color with black bands around the body and a wider blue band at each end of the body. Is the vine infected and does it need to be removed or can the grapevines be saved? The damage is done, but is there a preventative action I should have taken?
A: This is the grape leaf skeletonizer, a dark blue black moth that lays its eggs on the underside of grape leaves. They usually begin laying eggs around April and that’s when control measures need to begin.
The egg hatches and out comes a larva, fitting your description. This worm or larva begins to skeletonize, or nearly defoliate the grape leaves leaving behind the veins of the leaf. Hence the name, grape leaf skeletonizer.
Control is pretty simple and effective with organic pesticides containing Bt or Spinosad. Sprays should be applied in April prior to egg-laying or just after.
If you follow my blog via my newsletter or my tweets on twitter, I announce when to make applications like these ahead of time. Otherwise, just mark your next year’s calendar and make this application some time in the first two weeks of April, depending on the weather.
Make sure you spray the undersides of the leaves, not just the tops. The spray will work now as long as the larvae, or the worms, present. It doesn’t work on the adult moths. Your grapevine will put on new leaves to replace the damaged one so just be patient.
Q: It is my understanding that the ball growing in the middle of my sago palm is part of its reproductive system. However, since I do not plan on pollinating the plant, how and when can I remove the growth? Also, can you tell from the images if it is male or female sago?
A: Sago palms come as male or female. The flower or inflorescence of the male is long and cone shaped while the female is flat and disc shaped. That should be easy to remember. Yours looks like a female.
Normally this inflorescence is not removed and you let it run its course. I am not sure why you would want to remove it anyway.
Q: I have a large pine tree in my front yard. I trimmed this tree in the past and had buckets and buckets of sap coming from large limbs that were cut. I may need to prune heavily again this winter. But since I just completed relandscaping under it, I’m worried about all the sap that is going to fall on everything I just put down. I’ll never get off all the sap that will drip on everything.
Is there a way I might prevent or stop the sap from dripping such as pruning paint? Is there anything to save all my hard work from being completely encapsulated in sap?
A: Pruning paint might help in this case and may be worth a shot. Most people in the know no longer recommend pruning paints to cover wounds on trees. They just sanitize it and let it air dry.
The reason for not recommending pruning paint is because research has found pruning paints to be primarily cosmetic and do not assist the tree in healing. Healing is best if the wound is left alone without the use of paints.
There is some research that supports the idea that pruning paints may actually cause some harm to an open wound. But pruning paint will not kill a tree or severely weaken a tree. Compounds similar to pruning paints are still used in propagation of trees such as grafting and topworking.
In this particular case I would go ahead and try it since the benefits will probably outweigh any negatives to the tree.
Q: This is the first year my 7-year-old black mission fig is “behaving” strangely. The fruit came on, some even started to ripen, and now they are shriveling on the tree. The tree looks perfect and so do the leaves. I did read your article on figs but ours always seems to be treated the same, year in and out.
A: All of the cases that I have seen of fig fruits drying out on the tree have been from a lack of water getting to the fruits. This can be from a lack of applied water, plugging drip emitters, damage to the tree trunk restricting water to the fruits, or an increase in tree size without the application of more water.
The first response a fig tree has to inadequate amounts of water is for the fruits to shrivel. This typically leaves the rest of the tree unaffected. The leaves look the same; growth appears to be normal but usually with a smaller or open canopy.
A fig tree receiving enough water will have a dense canopy. Oftentimes the canopy is so full you are unable to see through it.
Not enough water to a fig tree results in a more open canopy. It is common for fig trees receiving enough water to grow 6 or 7 feet in one season.
My suspicion is inadequate water. Trees get bigger each year. You either have to add more emitters, increase the size of the emitters or add more minutes to the run time. I would focus on this rather than to water more frequently.
As a test, try supplementing the water the tree gets by adding water with a hose once a week. Create a basin under the canopy, level, about 5 feet across and several inches deep. Fill this basin once a week.
Also figs do much better if 4 inches of wood mulch is applied under the canopy in a circle around the trunk with a diameter of at least 6 feet.
Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.
