Rose Care FUNdamentals for August 2023

Frank Brines

ARS Master Rosarian

Summer is certainly upon us – and based on past experience, it’s only going to get hotter before it gets cooler. I didn’t need to tell you that at the beginning of August, did I? The year 2023 is and has been very unusual weather wise breaking records all over the globe.

Since high summer temperatures and less-than-ideal conditions for roses are inevitable for the next couple of months, let’s get ready. Stroll through your gardens in the morning, look for leaf wilt, drying or discoloring of leaves and the general leaf reflectance, which is called surface luster. If it appears dull, investigate the plant for disease, drought or pests.

If you’ve taken my advice, you’re letting your roses continue their summer dormancy until about mid-September. Struggling to remain hydrated will likely produce poor quality blooms. Just remove and discard the withered petals and let the hips develop, keep the bed clean of debris and don’t fertilize. Be sure your irrigation program is in good condition and delivering needed water. It doesn’t take long for a rose to suffer once its irrigation supply fails.

When temperatures range in the 90 F zone, roses like most living things perspire which requires intake of more water to keep cool and live. Roses “perspire” through cells along the edge of the leaf. If there is not sufficient moisture in the root zone, browning of the leaves results. It is a sign of heat stress and needs immediate attention. This situation also limits bloom size, color and appearance of burned crinkled petals. It is why as much as 12 gallons of water per week is needed for the rose just to survive let alone produce lovely beautiful blooms.

I suggest only removing the petals of any roses that bloom and any fallen debris. Do not fertilize and increase the water. Let the plant rest the best it can. In the event that foliage becomes so stressed from heat and turns brown, dead ones fall off. Be careful not to remove so much that the cane becomes unprotected from the sun and gets sunburned which could kill the plant.

I took a few photos in my garden this morning. I now live in an area that isn't quite as warm as the Temecula Valley so I'm sure gardeners have seen something similar in their gardens with the recent temperature records. The size and color of this rose is not typical of the variety due to the heat.

The sawfly is active now also. It is usually a minor character but can create havoc if left alone and becomes prolific. On new growth, it can kill the new vegetation. It’s also called the “cane borer” because it bores into a cane and lays eggs. I have these insects in my own garden; note the sawdust on the cane.

Chilli thrips are a year-round pest, but they love hot summer days best. They are 0.016 inches to 0.024 inches long, one fourth the size of the western flower thrip. Gardeners will know chilli thrips are present only when new foliage and blooms are already damaged. Blooms will be deformed, discolored and outer petals will be darkened. Buds will be distorted, darkened and may not open with misshapen distorted new foliage and bronzing on the back of new leaves.

Chilli thrips love all new foliage and bloom colors, unlike western flower thrips who prefer light colors. It’s astounding the amount of damage they can do in a very short time. Control is easiest in the earliest stages since a severe infestation can rapidly defoliate a rose bush and your other plants too.

During hot weather the life cycle for chilli thrips is 11 days. Part of that time is spent in soil or debris under the plants. The larvae stage molt into a pupal stage and usually enter the soil or debris to eventually emerge as adults. Only the larvae and adults are in the feeding stages. Adults are dispersed by wind over long distances.

Integrated pest management stresses the importance of cultural, mechanical and biological controls before resorting to the least toxic chemical control. Since chilli thrips have a short life cycle of 11 days, gardeners must detect damage and implement a method of control immediately.

Cut out damaged buds, blooms and leaves; remove all fallen leaves and petals from the garden. A natural hero in the fight is the minute pirate bug which feast on all stages of this pest, as well as on spider mites, insect eggs, aphids and small caterpillars. You can actually buy them online.

If chemical control becomes needed, choose the least toxic spray and follow label directions. During infestation, all new growth will need to be sprayed weekly. Conserve or Captain Jack’s Deadbug Brew concentrate are two organic sprays with active ingredient Spinosad. Spinosad will not harm ladybugs, green lacewings, pirate bugs or predatory mites. Spray early in morning or in evening after bees are less likely to be active and before temperatures reach the 80 F.

During the daily tour of the garden look for any changes. Examine the lower leaves. If they appear yellow or brown, have fine webbing and/or look dirty, there may be an infestation of spider mites. Some areas have experienced a real problem with spider mites this year. They thrive in hot weather. They’re generally found on the undersides of those leaves.

A quick check can be made by lightly running your fingers across the underside of the leaf. If it has a small grainy feel, it most likely is the spider mite. A strong spray of water from below followed by an overhead shower should take care of the problem or, at least, hold it in check. Give the shower early in the day so the plant has time to dry before the sun becomes hot. Do this every three days for 10-14 days, inspecting regularly. It may be necessary to repeat after a few days if the infestation is heavy.

Captain Jack’s Deadbug Brew is a good product to use in this case. Removing the bottom leaves approximately 8 inches from soil level can help in reducing or eliminating the spider mite problem. It should be done earlier, before an infestation.

The world is dangerous enough for plants, but gardeners are also faced with risks. One is a dangerous fungus with the scientific name Sporothrix schenckii. It afflicts humans with the fungus infection sporotrichosis which is often referred to as the Rose Thorn or Rose Gardener's disease.

The fungus resides on hay, sphagnum moss, the tips of rose thorns and in soil. It can cause infection, redness, swelling and open ulcers at the puncture site. The fungus can also spread to the lymphatic system and move on to the joints and bones where it ends up attacking the central nervous system and lungs when the thorn or thorns are deeply embedded. A relatively uncommon condition, diagnosis can be complicated. Physicians often mistake it as staph or strep infection. Be sure to inform your physician that you are a gardener so appropriate diagnosis and treatment are rendered.

Many people enjoy the fragrance and beauty of roses, and gardeners have often had their skin pierced by thorns.“Prickles” is the correct anatomical name. Good protective measures include wearing appropriate clothing, such as gloves, long sleeves or gauntlets, when working among roses and thoroughly cleansing even minor scratches and punctures with an antibacterial soap. Rubbing alcohol – which you should already have handy to clean your pruners – can be applied as an immediate wash until you can use antibacterial soap.

Anything more than a minor puncture should be watched carefully for signs of infection; seek medical attention as soon as possible if you show any of the signs described above. Even the simple things in life have risks – take precautions so you can stop and smell the roses. And when you’ve got a moment to spare, go visit Rose Haven, 30592 Jedediah Smith Road in Temecula. The cross street is Cabrillo Avenue. Also, visit http://www.TemeculaValleyRoseSociety.org.