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ROSE CARE FOR SEPTEMBER
WESTERN ROSE CURCULIO, PART II
by Betty Mott, Master Rosarian
Prevention and Control Measures
There are many options to consider when dealing with Rose Weevils (Curculios) Merhynchites (=Rhynchites) bicolor Fabricius.
First: Be on the lookout as early as March through mid June. Climate and weather have a lot to do with the timing of emergence of the adult beetles from the soil. It might be earlier or continue on later depending on where you live. Hand picking and the destruction of the adults as they appear on the plants before the injury is done is the goal. Record in a garden journal which bushes were infected and when they first appeared so you are prepared for the next year. Remember if you missed removing any damaged buds or flowers with eggs, they will be right back emerging from below those rose bushes next year. Removing the injured buds and destroying them prevents the development of the larvae and gives protection for the following year.
Second: The destruction of the overwintering larvae in the soil. “Parasitic nematodes can be used against rose weevil larvae provided that larval populations are located prior to spring emergence. Gardens where the infested buds are allowed to fall to the soil would be prime candidates for this biological control method.” More detailed information on where to get parasitic nematodes and how to apply them is listed at the end of this article.
Third: “Rose buds or entire rose bushes can be protected using a netting material that allows sunlight and water to penetrate but excludes insects. Bonnets can be made with a material called "remay."
“If the above control methods do not achieve satisfactory control, chemical insecticides may be considered for larval and adult weevil control. If a larvae are recovered from the soil, insecticides registered for soil use can be used around the rose bushes in order to kill the soil inhabiting larvae and emerging weevils. Insecticides can also be sprayed at the first sign of the weevils presence in the spring. Insecticides used in the control of beetles on roses and other ornamentals should work on these weevils. Please check the label and read all the precautions on the insecticide label before using any insecticides.”
Not everyone agrees on the effectiveness of the above methods. You, as the rose gardener will need to select the best plan of action that works for you. How much time and money you want to commit, and whether your garden is chemical free will be your determining factors.
One study reported that hand picking cannot be relied upon as a control of a pest of this kind because at best it reduces slightly the number of adults; since some beetles escape by dropping to the ground, and others are overlooked because they might be out of reach. If clumps of roses are near the plants to be protected they will furnish an almost continuous supply of beetles which will sooner or later find the prized plants and destroy many of the buds. If the picking is carried out daily, the beetles may find their way to the plants shortly after the operation has been carried out and destroy many buds before the next picking time.
Under another study liquid sprays of paris green and lead arsenate gave some protection, but much less when materials are applied as dust. Of the poisons applied the calcium arsenate gave the quickest kill. It was found that the beetles crawling over the dusted roses, became covered with the dust, the dust sticking on their feet and within a few minutes the beetles were seen cleaning their feet and legs. The antennae were cleaned by pulling them through the mouth parts, thus obtaining a lethal dose. For larvae control an emulsion of carbon disulphide was used but the strength used must be carefully calculated to avoid the leaves dropping off or drooping after application.
Long term use of any chemicals and their side effects on humans, pets, and other wildlife should be considered. For me chemicals are not an option so I will add the two applications of the beneficial nematodes to destroy the larvae in the soil.
History of Western Rose Curculio in Mill Valley, California 2009- 2013
2009- Notes from my journal included droopy buds and open blooms riddled with small holes on my hedge of 6 ‘Cecile Brunner’ roses and ‘Alchymist’ a once blooming shrub rose. Note these are two of my first blooming roses. No action was taken.
2010-After noticing the lady bug look-alike with a piercing snout I began trying to catch and squash the insect afflicting the damage. They were winged, fast, and ducked to avoid me when disturbed, eventually dropping to the ground out of sight camouflaged in the mulch. After noticing their behavior I came armed with a mug of soapy water taped the insect and gleefully watched it drop into the soapy water sinking to the bottom. Unfortunately they had moved to another rose bush ‘Topaz Jewel’ HRg, and continued to multiply on the ‘Cecile Brunner’ and ‘Alchymist.’ Hunting for curculios became a daily practice several times a day from late April through May the prime of my spring bloom cycle. The only relief was knowing that they only have one cycle a year and would disappear.
2011- Friends who live in Tiburon were fighting the same battle on their roses along with an alarming increase of thrip and coddling moth on their fruit trees. These backyard composters, with a chemical free garden began to research alternatives to controlling these insects raising havoc in their mature garden. And so they would connect with the Gardening Zone to have a custom blend of beneficial nematodes costing $79.95 consisting of Heterorhabditis Bacteriophora and Steinerema Carpocapsae 50 million to be exact to be applied to their garden. In early March a clean garden sprayer was used to apply the nematodes. After one application they noticed a marked improvement in the reduction of thrip, curculio, and coddling moths. They continued to apply the nematodes twice a year once in the fall (November) and March noting fewer curculio ( 2-3) in 2013.
2013-Motivated by success my Tiburon friends and I decided to do two applications of Nematodes one in November and one in early March. We were able to get a two for one special sale in November bringing the cost down. I increased my number of nematodes to 50 million and we both decided to add another 25 million specialized nematodes Steinernema feltiae to combat root knot galls, fungus knat, and sawfly, since we were both seeing sawfly damage on our leaves. My friend used a sprayer and I used the watering can method of distribution which took two or more hours. I remember Baldo Villegas saying, “Cecile Brunner” is a curculio magnate! He decided to remove them from his garden seeing them as a prime host. I was not ready to do that since the rose bushes date back to the early 30’s when our property was part of a dairy farm in Mill Valley. The curculio made their first appearance in early March this year, but just a few. I was relieved and thought I had found a cure. Then April 27th a few more appeared. I began to remove all drooping buds or blooms showing any damage and disposing of them in the garbage can. Knowing the eggs of the next generation in the life cycle were in place I was not going to take any chances. Although my numbers were way down I wanted to take it to the next level of prevention. Since they are winged I was still not sure if they were coming in from my neighborhood or emerging from my soil. Again daily walks through the yard, squishing them and removing and disposing of infected buds all through the month of May. The mating process was more prominent mid to end of May. The last curculio was spotted the second week in June. I went through all my climbers deadheading, making sure all the infected buds were removed and in the trash. My 2014 garden journal will record the story of my success or reveal the necessity for another level of action and research.
Data gathered from Marin Rose Society Consulting Rosarians
With 17 reports all but two had curculio this year ranging from only one to total infestation described as the “Most ever in their rose gardens.” Our Marin Rose Society Public Rose Garden in Ross had significant first bloom damage with eggs and larvae found in the infected buds. Handpicking was the most common method used, along with removal of damaged buds and blooms. Soapy water, squashing with fingers, suffocation in plastic pill containers, removing with gloved hands, squishing with rocks, along with knocking off with water were some of the other methods used. I was the only rosarian using nematodes. ‘Sally Holmes’ seemed to be a curculio magnate in several rose gardens in 2013. Light colored roses seemed to be the first preference. Although in cases of heavy infestation, ‘Mr Lincoln’, ‘Color Magic,’ ‘Bonica’, ‘Fragrant Cloud’, ‘Chicago Peace’, ‘Gold Medal’, ‘Morden Sunrise’ and Austin’s regardless of color and miniatures were eventually targeted. Bursts of heat seemed to bring them out.
Information on Beneficial Nematodes
There are several distributors on line who will ship nematodes to you. Some local garden centers carry them refrigerated along with the ladybugs and praying mantis. I used http://gardeningzone.com/ because they are shipped to you in two days from the order date. They arrive in a cooler with ice packs and will need to be distributed immediately or kept cool in the refrigerator and applied within a few days. So plan ahead before you place your order. This general information about Beneficial Nematodes was taken from the Arbico Organics Natural Solutions website - another company who ships to your house. http://www.arbico-organics.com/
Conditions: Remove from shipping bag or box and store the container of nematodes, unopened in a refrigerator. Use as soon as possible.
How Do Nematodes Work?
After application, the nematodes immediately get to work. Upon finding a pest, they enter it through various body openings or directly through the body wall. Once inside, the nematode releases a toxic bacterium which kills the host larva within 24 - 48 hours. The bacteria creates a food source and a hospitable environment for the nematodes to reproduce. As the food resources within the dead pest become scarce, the nematodes exit and immediately begin searching for a new host.
How Are Beneficial Nematodes Applied?
It's easy to apply nematodes:
Before applying, make sure the soil is moist. Cloudy days are perfect. Early Morning or late afternoon or when temperatures are not extremely hot.
Mix nematodes with water, allow to sit for 5 minutes so that the media dissolves completely.
Apply using a watering can, hose end sprayer, backpack or pump sprayer or through irrigation or misting systems.
Lightly water again after application.
When Should Beneficial Nematodes be Applied?
Since nematodes are sensitive to light, apply them early in the morning or at dusk. Use beneficial nematodes whenever pest larvae or grubs are present, during the spring, summer and fall months. As pest larvae feed on plant roots beneath the soil surface, severe damage can be done before you realize you have a pest dilemma. If adult insects are present, their eggs, nymphs, larvae and pupae will soon be developing.
For Prevention: Apply at least 2-3 times per year in the spring, summer and fall.
Optimium Release Temperature: Apply when outdoor/indoor ambient temperatures range from 45° to 105° F pre-dawn or at dusk. Water before and after application.
When Will I See Results?
Nematodes are considered to be one of the most lethal parasites known to kill plant pests. Depending upon the pest(s) you are treating, it can take from 2-30 days for you to see results. You will not see dead insect bodies.
Selecting the Variety of Beneficial Nematodes:
Steinernema carpocapsae Mobile Pests: Fleas, caterpillars, cutworms, armyworms, sod webworms, fly larvae, worker/soldier ants, worker soldier termites and more.
Steinernema feltiae Mobile Pests: Fungas gnats, ticks, thrips, leaf miners, onion maggots, root maggots, subterranean termites and more.
Heterorohabditis bacteriophora Stationary Pests: Grubs, root zone weevils, citrus weevils, Japanese beetles, black vine weevils, rose weevils, ticks, queen ants/ termites and more.
It is best to call the company and make sure you are getting the correct mix of nematodes for your particular garden pests. I will report my progress next spring, 2014.
Bibliography: Villegas, Baldo. http://www.sactorose.org/
Cassidy, James Notes on Miscellaneous Insects
Cockerrell,T.D.A. Rhynchites bicolor, Essig, E O. Insects of Western North America
Gillette, C. P. and List The Western Snout-Beetle, Green, J. W. Notes of American Rhynchophora
Leng, C. W. Catalogue of Colcoptera of America
A YEAR OF ROSE CARE:
July and August
November and December
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Last Modified: 09/16/13