[Arid_gardener] Roses dying

RodMcQ6@aol.com RodMcQ6@aol.com
Fri, 22 Sep 2000 19:08:59 EDT


Roses are a member of the same family as pyracantha which is quite 
susceptable to fire blight, however I've never seen Fireblight on roses in 
the low desert.  The tell tale symptom of fireblight is that the canes will 
look as if they were burned with a blow torch. Rust and blackspot are very 
seldom seen on roses in tthe low desert. The only fungus that we have to 
contend with is powdery mildew. For this we are thankful.
The symptoms that you describe  is fairly common in the low desert, but to my 
knowledge has not been named. I have lost several roses this summer to those 
same symptoms. Recently I sent a rose dying with those symptoms to the Univ. 
of Arizona pathology lab in Tuscon. They were unable to find a pathogen that 
was causing the problem.
     Yesterday at a rose society meeting I talked  with four other Consulting 
Rosarians about the problem that we all encounter, one that you described, 
and we all agreed that the problem is caused by high temperatures, wind and 
sun burn and inadequate irrigation. Even with adequate irrigation there may 
be times when the rose is not able to take up enough water to satisfy its 
need.
      Most of the rosarians that are growing roses for show  are doing some 
things to help the rose handle our hot summers such as;
Covering their roses with shade screen.
Wash down or mist their roses often, daily if possible.
Cover the rose bed with a 3 or 4 inch mulch.
       I'm enclosing an article that I coauthored on summer rose care, I hope 
it will be helpful.
      If you live in the east valley I'd like to extend an invitation to 
attend the  Mesa East Valley Rose Society meeting which will be held at Mesa 
Community College, student center, Kiva room at 7.00 pm on Oct. 12.  If you 
can attend you will pass by MCC's  rose garden with over 3000 Roses.

Good luck

Rod McKusick
Master Gardener and Consulting Rosarian


                                  SUMMER ROSE CARE  

        The summer months are especially tough on roses, however, here are 
some tips to help them  survive our hot weather.

       Roses need to be watered frequently and deeply. Water at least twice 
each week, and if they look stressed, water again. Deep watering will 
encourage the roots to grow deeper and will also flush the salts below the 
root level. 

      Roses in containers will have to be watered several times a week.  As  
long as you have good soil, a combination of one-third native soil, one-third 
mulch and one-third sand, perlite, peat moss or pumice, you'll have good 
drainage and you won't over water.

        Roses also need to stay cool. Use three to four inches of good mulch 
around each rose bush. You can use compost, peat moss, forest mulch, straw or 
bark chips. This will not only keep the root's cool, it will also conserve 
moisture, cut down on weeds and help too built a good healthy soil structure.

        Roses are heavy feeders and need some fertilizer during the hot
summer. A slow release granular fertilizer works well and usually lasts about 
six weeks.  Use one-third to one-half cup for each standard size bush. 
Scatter the fertilizer around the drip line. Water well before and after each 
application to prevent burning the roots.  You can also use a water soluble 
fertilizer, such as Miracle Grow, Peters or Magnum Grow, but this will need 
to be applied every two weeks. In the summer, use  one-half the amount you 
would normally use. Again, water well before and after applying the 
fertilizer.

        Roses slow down during our hot months and produce smaller and fewer 
blooms.  Cut off spent blooms, cut back to the first five-leaflet set, leave 
as much foliage as possible. The foliage will  help to shade the bush. 

        Watch for sucker growth, these are canes that come from below the bud 
union. They appear different from the other canes. Cut them off below the bud 
union.

        
         
        The hot dry weather will bring a variety of insects Watch the lower 
leaves for spider mites. The lower leaves will be lighter and have a fuzzy 
appearance.  The underside of the leaf will feel like sandpaper.  The spider 
mites suck the juice from the underside of the leaf. To control them,  remove 
the damaged foliage and use a strong spray of water every other day. If this 
does not take care of them, there are several effective miticides on the 
market.  Remember to read and follow directions on thecontainer.
        
      Aphids are the most common of the insects affecting roses.  They can be 
green, brown or reddish brown. They suck the juices from the bush and leave a 
shiney sticky substance on the leaves. To get rid of  them use a  strong 
spray of water every day.
        
       Thrips are probably the most damaging of the insects.  They are tiny, 
brownish yellow winged insects. You can barely see them.  They enter the bud 
and eat on the flower petals, causing them to turn brown.  The only way to 
control them is to spray the buds before they open with a good insecticide.  
Besure to read and follow directions on the package.
        
      Leaf cutter bees will make semicircles in the rose leaves.  They
use the leaf circles  to build their nests. The damage to the plant is 
minimal, and the bees are important pollinators, so there is no need for 
control.

        Other problems to watch out for are nutrient deficiencies. The most 
common is iron deficiency. The leaves will be pale green or yellow with dark 
green veins. Add chelated iron (FE 138) according to package
directions.

     Nitrogen deficiency is characterized by yellowing of the leaves,  
reduced growth, weak and spindly stems.
 
      With a Potassium deficiency the older leaves will turn yellow and then 
brown, sometimes purple.  New shoots will harden , stunted  and flower buds 
may become distorted.

      Phosphorus deficiency will cause older leaves to drop without turning 
yellow, leaves appear dull grey-green and may cup down.

     Manganese deficiency is similar to iron chlorosis in that there is 
interveinal chlorosis.  The small veins remain green with a netted appearance.

      Zinc deficiency causes new growth to stop and also causes distorted 
chlorotic leaves.

      These problems can all re corrected with a good rose fertilizer.
Maintaining a good soil PH of 6.0 to 6.5 is ideal for growing good roses.

      The best way to take care of your roses in summer is to make sure they 
have enough water, mulch, light fertilizer and  wash off  the leaves and 
stems in the early morning  with a strong spray of water at least twice a 
week. Be sure to get the underside of the leaf.  This will keep the roses 
clean, increase the humidity and will help to control insects  before they 
can cause any damage.  
        
      Watch your roses throughout the summer. Keep them cool and well watered 
and they will reward you with beautiful blooms in the fall.

Marylou Coffman 
Master Gardener and Consulting Rosarian

Rod McKusick
Master Gardener and Consulting Rosarian