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Rose Culture Tips for June, July and August
Guest Author: Baldo Villegas, ARS Consulting Rosarian/Entomologist
Sacramento, CA (USDA Zone 8/9)

Thanks to the never ending rain and prolonged cool weather in April, I am still enjoying flowers from the first bloom cycle. The second bloom cycle is not far behind as it normally starts towards the end of May. This prolonged unusual weather was challenging especially with the widespread occurrence of fungal diseases like blackspot, rust, stem cankers, and even botrytis on the stems, leaves and blooms. The weather is turning back to normal and temperatures are predicted to reach 90º F by Memorial Day weekend.

DEADHEADING has been my top chore in the garden lately. This is the process of removing spent bloom including the unopened buds and flowers infected with Botrytis. Yes, Botrytis was a huge fungal pest this year due to the hail damage and prolonged cool wet weather. This fungal disease rotted the blooms before they had a chance to open. Even with this nice weather, petal infection continues and blooms infected with it must be removed. In newly planted roses I tend to cut off the bloom just above the first 5-leaflet leaf that points towards the outside of the plant. I try to preserve as much of the foliage as possible. In well established bushes I prune down the stem until I see the thickness of a pencil and then find outward pointing leaves and I cut above them. The angle of the cut and the height above the leaf is really not important as some rosarians lead us to believe. While deadheading I also do a light pruning by removing dead wood, unproductive canes, canes infected with canker, any crossing canes, excess growth from the center of the plant, as well as blind shoots. Why leave this for the winter when I can take it off now? I am careful not to take excess growth as the plants need the foliage to produce food and from protection from the sun.

As I am deadheading I also watch out for potential pest problems such as SPIDER MITES. So far I have not seen any signs of an infestation in my rose garden. In some of the shady areas in the back yard I did notice leafhopper damage which can be easily mistaken for spider mite damage. Spider mites are usually present in one's garden all the time. If we overuse broad spectrum insecticides such as Orthene, the natural enemies are killed off and the spider mites are not kept at low levels. As the temperature starts to climb up into the 90's check the roses in the areas of the yard that are the hottest! Look for the diagnostic leaf stippling which they produce by their sucking mouthparts then turn the leaves over so that you can see the undersides and look for the presence of silken webbing which they produce as nesting material. If you spot this type of damage take immediate action otherwise the roses will loose their foliage if the infestation is severe. Miticides or pesticides that kill spider mites are very expensive and hard to get. Ortho has one under the Isotox Formula IV formulation which contains Hexakis (Vendex). Insecticidal soaps and horticultural oils can also be used but these are contact action pesticides and you need to get under the foliage and to get a thorough spray where the spider mites are located. Because of this I normally leave chemical control of spider mites as a last resort and let my irrigation system control them. If I see a new infestation starting, I place extra misting emitters from my drip line under infected plants and let the emitters wash the foliage from underneath the plants

DISEASE CONTROL is especially important this year due to the prolonged cool and wet weather that we experienced during April and early May. I started using combinations of Immunox, Daconil, and Banner Maxx this spring with excellent results. I prefer Immunox to Funginex as it is safer - The Signal Word is "Caution" and not "Danger" as in Funginex. Also, it is cheaper, especially if one shops at places like Lowe's, OSH and Home Depot. Due to the constant bad spraying weather and my traveling schedule, disease control got away from me and now I have a major infestation of BLACKSPOT and RUST. For these diseases I will continue the above treatment alternating Daconil with Immunox/Banner Maxx. I also bought a new "Spotshot" sprayer system from Robbie Tucker's website, http://www.rosemania.com/ which will be arriving hopefully by Memorial Day weekend. This battery powered sprayer has a 7-gallon tank, and is mounted to a dolly-type frame that is easy maneuverable, and comes with a 50 foot hose so that one can park the sprayer in a central place and cover a 100 foot area. Robbie highly recommended the use of Manzate or Mancozeb in order to control blackspot. I will be checking about their availability in California through places like United Horticulture Supply in Sacramento and Pacific Turf Supply in Rocklin.

FERTILIZING our plants is a chore that is often forgotten during the summer months. If you haven't applied some of the "organic" fertilizers, this is your time. I usually like to apply at least one application every six weeks of some of my favorites like fish meal, fish emulsion, alfalfa meal, or any of the "organic" fertilizers as directed in the label instructions. Please water the plants well before and after applying any dry fertilizers in order to avoid fertilizer burn to the plants. I supplement this with applications of water soluble fertilizers applied from a water hose applicator. I usually buy the 20-25 lbs bags of 20-20-20 water soluble fertilizers from places like United Horticultural Supply in Sacramento. WalMart's Deep Feed and MiracleGro are other water soluble fertilizers that have given me excellent results. If I am preparing my garden for a rose show or a garden event I shorten the application interval to about every two weeks starting about 7 weeks before the rose event. I like to apply these water soluble fertilizers during the day so that the foliage has a chance to dry within a couple of hours in order to avoid development of fungal diseases such as blackspot and rust.

I still have not had a chance to apply my MULCH on the rose beds. This is another of my top priorities by the end of May. I generally get about six yards of shredded redwood/cedar bark to cover my entire rose garden at the depth of 2-4 inches. It takes a couple of days to get it spread around the rose beds so this Memorial Day weekend will be my targeted weekend for this chore. A good thick layer of much is needed in order to keep the soil cool, preserving moisture in the soil, and prevent weeds from germinating.

While in the subject of WATERING, don't forget to make sure your irrigation system is in good working order. Drip irrigation and sprinkler systems each have their pluses and minuses. If your fungal diseases mentioned earlier are out of control, avoid sprinkler irrigation until they are under control. Roses need deep watering down at the root level. Make test holes and check for moisture at the root zone and water accordingly. If you have potted plants water them on a daily basis. Depending on the exposure and the soil composition in the pots, some potted plants might need to be watered more than once per day.

This is the time of the year when BASAL CANES are actively being produced by the plants. One suggestion that was made by Johnny Becnel at the recent American Rose Society National Convention in New Orleans is to pinch the new buds that are formed in order to encourage branching later on in the season. In climbing roses new basal canes might need to be trained so they can be bend or arched in order to maximize bloom production. STAKING them early will prevent breakage of valuable canes. When tying canes down use plastic tape or wire ties that have plastic insulation. Do not tie down you canes too tight, as this may damage the canes.

Lastly keep track of the performance of your roses in a notebook or a database. Keep a calendar of your spraying activities, mixtures, etc., as well as your fertilizing dates. These records will allow you to get rid of nonperforming roses and which roses do best in YOUR GARDEN and make adjustments to your rose culture program in the years to come.


Last updated: 3/7/09
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