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Rx FOR HEALTHY ROSES - WRAPPING IT UP
As the days shorten and temperatures drop, the change in the season is evident. In most years, it’s likely your roses would be ready to put out another round of bloom before they, like you, tuck it in for the winter. But with the heavy rains of late June, mild to cool temperatures throughout the summer, and bountiful fog that managed to keep foliage damp, conditions have been ripe for some of our rose’s arch enemies, particularly blackspot. If you’ve still got leaves adorning your plants and they continue to push out new flowers, whatever you’re doing to maintain healthy roses seems to be working.
by Nanette Londeree, Master Rosarian
During the past ten months in this column, we’ve covered lots of options for keeping roses healthy by employing an integrated pest management (IPM) approach. Managing your garden using IPM involves determining how much damage you can tolerate, observing the garden for pests, diagnosing the problem, implementing a pest management strategy and evaluating your program’s effectiveness. We looked at the major categories of rose pests including chewing and sucking insects, the nasty diseases - blackspot, rust, downy mildew and powdery mildew, the biggest pest, deer and ubiquitous weeds.
The integrated approach for management of any of these pests follows the IPM pyramid – beginning with the least toxic method - cultural, then moving up the pyramid with mechanical, biological and finally, chemical methods. There is also the “do nothing” method, where the damage from the pest is either so low, or the cost / risk of an effective control measure is so great, that no action is needed or desired. You were introduced to a wide spectrum of treatments, many that are new and cutting edge, with examples of specific remedies identified by name (not intended as a product endorsement). Some of the highlights from the past months include:
Cultural methods – selecting plants with known disease resistance, planting in an area with plenty of sun and air circulation, developing healthy, well-draining, friable soil, providing adequate water at the appropriate time and method, supplying a balanced level of needed nutrients, pruning plants to maintain vigor and promote good air circulation, mulching to conserve water and reduce weeds, removing debris and infested plant material and providing habitat for natural enemies.
Mechanical and physical methods – a blast of water can knock soft bodied insects to the ground and keep powdery mildew and spider mites at bay. Picking off larger visible pests like curculio weevils or cucumber beetles and dumping them into soapy water can reduce their populations and related damage. Pruning off heavily infested portions of a plant is an immediate and effective remedy for caterpillars. Topping soil with a hefty level of mulch can reduce weeds and a sturdy fence will keep the deer outside the garden, just able to look at, and not eat those precious blooms.
Biological methods– providing habitats to encourage natural enemies like lady beetles, lacewings and syrphid flies along with generalist predators (birds, beneficial insects, toads) can keep many insect pests in check. Microbial based products such as Dipel DF that are pathogenic for a range of caterpillars and leafrollers, can be effective along with species of beneficial nematodes that may offer control for some types of caterpillars, leafminers and rose chafe.
Chemical methods– the options in this category are huge, and include many innovative new products. Beginning with the least toxic types, there are:
Horticultural oils and insecticidal soaps - Sun Spray’s Ultra-Fine Horticultural Oil Spray is a parafinic-oil product that can be used year-round to smother a wide range of pests. EcoSmart Garden Fungicide, a contact fungicide, is a blend of rosemary, thyme and clove oils labeled for control of anthracnose, blackspot, botrytis and rust. Clove oil is also the active ingredient in Matran 2 from Bioganic® Crop Protection, a post-emergent, Organic Materials Review Institute (OMRI) listed herbicide. Garden Safe Brand Rose & Flower Insect Killer contains potassium salts of fatty acids as the active ingredient along with a small amount of ethanol and is purportedly effective at managing aphids, leafhoppers and thrips.
Another group of chemicals utilizes plant derived materials like neem seed extracts, and pyrethrum. Neem seed based products (with the active ingredient azadirachtin) are labeled for use on roses for managing chewing insects - bristly rose slug, earwigs, grasshoppers, tent and orange tortrix caterpillars, leafrollers, bud worms, rose curculios, and rose chafers.
Chemical treatments that are derived from nature are increasingly available. Botanigard ES is labeled as an “emulsifiable suspension mycoinsecticide” which roughly translates to a liquid containing a fungus that is targeted for control of aphids and thrips. BASF’s Serenade is a biological based fungicide that, when sprayed on the plant, destroys fungal pathogens and helps prevent powdery mildew from infecting the plant. Similarly, Actinovate by Natural Industries, contains a high concentration of a patented beneficial microorganism that grows on the plant’s roots and leaves while attacking harmful disease causing pathogens.
A relatively new class of chemicals, the strobilurins, is based on a natural, anti-fungal chemical produced by a Basidiomycete fungus. BASF’s Pageant, with the active ingredient pyraclostrobin, claims to be “a broad-spectrum fungicide combining two fast acting active ingredients, boscalid and pyraclostrobin, into one product that offers more control on more diseases than any other currently registered fungicide.”
Pyrethroids are synthetic products that have a similar mode of action to naturally occurring pyrethrins. Bayer’s Advanced 3-in-1 Insect, Disease & Mite Control is a triad of chemicals aimed at insects, mites and disease. The insecticidal active ingredients are the pyrethroid fluvalimate along with a neonicitinoid imidacloprid; the combination controls a wide range of pests.
Locally systemic pesticides like Gowan’s Rubigan, in the pyrimidine class of chemicals, is for prevention and treatment of powdery mildew. The label on Ortho® MAX Flower, Fruit & Vegetable Insect Killer claims that this synthetic product kills 100 different pests including most of the chewers! The label also indicates it is toxic to wildlife and bees. It is an organophosphate, the same family of pesticides as Orthene and Malathion.
Some of the fungicides once commonly used by rosarians have been superceded by more effective, less hazardous materials. Use of products containing triforine (Funginex), captan (Captan 50WD) and chlorothalonil (Daconil), though still available, are most likely not warranted due to their more environmentally hazardous nature.
Now is a great time to evaluate roses growing in family, friend and neighbor’s gardens and assess their overall health. If you like what you see, find out what they’re doing; their practices might just fit into your pest management approach. And, if your garden is brimming with healthy plants and oodles of blooms, then keep up the good job, and enjoy the rest of the season!
Photo of ‘Candyland,’ is by the author—taken in the author’s garden in August, 2011.
Author’s disclaimer: Inclusion of a product in this series of articles does not constitute endorsement either by the author or the Marin Rose Society. Products are included for informational and descriptive purposes only.
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Last Modified: 08/06/2013