Caring for roses and treating pests

Frank Brine

ARS Master Rosarian

There were signs of climate change again this year. Seems as though confusion is the new weather normal. Temperatures and rainfall patterns differed greatly. Rose growth and development are dependent on weather, and flower production is particularly impacted by inconsistent temperatures, sun and water. All of this has made it more difficult for me to predict what to do and when to do it!

The longer time frame for rain and more misty cool nights caused some rust, mildew and botritis fungus to appear quickly. Blooms were affected by botritis which rots the petals preventing them from opening successfully. A few warmer days would encourage growth and produce buds, then a few days of 70-80 degree temperatures caused a burst of growth toward blooming. At least one application of fungicide spray helped to reduce the outbreak.

I completed pruning earlier than ever this year and my blooms were not that much earlier than previous years but peaked before the scheduled rose shows. The first roses bloomed about eight weeks after pruning. Typically, the first flush of blooms is expected after eight to 10 weeks, usually on the longer side. Those rose bushes are now in second blooming. In this area, the first annual rose shows are usually about now, and I know that other local exhibitors' roses are in all different stages of bloom, many past exhibit stage.

Abundant sunshine and water produce larger blooms, so your roses are probably really growing. If you didn't apply fertilizer earlier, be sure to do so soon (more about this a little later), along with plenty of water to maintain this production curve. Know the soil composition in your garden so you know how much water to apply to maintain good soil moisture without drowning the roots-or wasting water, given that we're hearing that the Southwest is in the driest climate cycle in 1200 years!

Be vigilant for changes, diseases and pests in your garden now, and be prepared to act on these immediately. The Hoplia beetle appeared in April with a few hot days. I usually see this beetle in May. I think we can now expect it in April so mark that on your calendars for the coming years. It can do serious damage in a short time to rose blooms. It can first be seen on light colored blooms.

The Hoplia is easy to remove when found by dragging it out from between the petals with a screwdriver or Q-tip and plopping it into a cup of sudsy water. (Note: To learn to identify Hoplia beetles, just do a search on the Internet. Bottom line however: If you find little holes in light colored petals, and you find beetles nestled between the petals, you've probably got Hoplia – dig 'em out!)

Another early visitor is the spider mite. Damage can be done well before you recognize it. If you suspect they are present and on your roses, an inspection of the underside of the leaf may assure you. They are very tiny and hard to see but when you run a finger lightly over the underside of a leaf it will feel gritty. The use of a sheet of paper can be used also. Use the paper to shake the leaf or scratch then onto the sheet of paper. If you miss the first phase you will see an unusual mottling of the leaves as seen from the top of the leaf.

Blooms mature quickly in warm weather, so as they fade, lightly prune back to the first outward facing five-leaflet leaf. Don't shorten the cane too much. If you remove just the blossom and peduncle (this little length of stem that ends at the blossom), you may get two weaker shoots with less bloom quality. This light pruning sets the stage for the next bloom cycle in about seven weeks.

For best production, try to shape the bush to outward facing buds. If you can, keep canes that are larger than the diameter of a wooden pencil. Doing all this now, your next blooms will appear around mid-June before the summer heat. Knowing this can help you prepare for a hot summer in Temecula Valley. Make sure to put all vegetation into your green waste barrel.

Roses want a constant supply of nutrients, including micro nutrients (copper, iron, manganese, magnesium, etc.). Remember that you are also feeding the soil microbiology, which is complex and multi-tiered, abundant in beneficial microbes which create a sustainable soil diversity acting like an "immune system."

Phosphate (N) and Potassium (K) help develop strong root systems, better blooms, and help prevent stress during adverse conditions. In fact, plants grown with organic fertilizers are themselves more resistant to pests and diseases. A soil test kit for analyzing the soil needs could save you lots of money, energy and guesswork for a fulfilling garden.

Organic amendments such as manure, compost or mulch stay where you put them, break down slowly, don't contribute to groundwater pollution (as long as you prevent run off into drains), improve the soil food web, so that in the long run you end up using less product while providing "food" for all the creatures like earthworms who act like rototillers mixing them into the soil to lower depths. The best thing you can do for your garden is to add a generous layer of mulch that doesn't have wood chips.

Keep an eye for worsening conditions such as water stress, insect pests, and fungal diseases. Do not use a formula that treats everything. Use only a product especially for the specific problem, and treat it in proportion to severity, as well as your level of acceptance. If control is lost it may be necessary to strip off all of the diseased leaves and prune back and basically start over.

Some organic formulas use neem oil, insecticidal soaps, baking soda, etc. Read entire labels and use according to directions, including safety equipment to avoid exposure to contaminants. Keep your skin covered when applying chemical treatments. Use approved goggles for eye protection, respirator mask, long sleeve shirt, water/chemical resistant boots and gloves. When the treatment is completed, immediately remove clothing and wash. Take a good shower to remove any possible contamination.

Gardens are showing increased prevalence of the fungal disease "Black Spot." It appears as dark green to black spots on leaves, which often turn yellow and fall off. The infected leaves (even those that fall) produce spores that can infect other leaves. There are many fungicides available, but control can be difficult. Sometimes you just have to remove and dispose of any affected leaves.

Another pest is the chilli thrip. It's much smaller than the Western Thrip we're accustomed to and more devastating as it eats all varieties of vegetation. Control is quite difficult and new treatments are being studied. Products containing spinosad bacteria seem to help control soft-bodied larvae but be aware that even such "natural" products can kill other (beneficial) insect species. Some gardeners are reporting chilli thrips in their gardens already. I have seen some evidence of thrips too.

It is never too late to apply a thick layer of mulch! Use composted mulch, not wood products. (Pine needles are good too.) Apply to a depth of 3 to 4 inches. Mulch keeps the entire bed uniformly supplied with water. Avoid mulch containing wood chips of any sort: Their breakdown robs the soil of nitrogen, and a mold can grow that is impenetrable by water, fertilizers, and oxygen.

Heads up for high summer: Don't expect great roses during July-September when temperatures are high. Just keep plants well hydrated, and remove just spent petals, leaving the "hips" (don't prune). The plants will enter a short dormancy and build strength for fall.

I am an ARS Certified Master Rose Consultant. If you would like personal answers to questions, you can leave questions on http://www.TemeculaValleyRoseSociety.org or write to me at [email protected].