My roses have the summertime blues. Is there a doctor in the garden?

For The Union-Tribune

Diagnosis to a problem is always key. When we feel out of sorts, it is helpful to check in with the doctor and find out if we should be worried. Likewise, when rose blooms or leaves look different, strange or are displaying signs of distress, it is helpful to know whether we should be concerned. If concern is warranted either for us or for our roses, a diagnosis gives us the direction upon which to base our remedial strategies.

Bloom questions

Q: The blooms on most of my roses this summer have been smaller than usual. I also noticed that this summer my multipetalled ‘Rock ‘n’ Roll’ hybrid tea rose has some single-petalled blooms. I am also noticing that some of my roses have blooms that look “crispy.”

A: Rose blooms and petals are often the plant’s first visible tipoff to us that our roses are experiencing heat stress. In hot weather, blooms are often smaller in size, multipetalled roses may have fewer petals than they typically have, and there is usually a reduction in bloom production. The color of some blooms will fade. And on some roses and especially the darker-colored varieties, petals can totally “fry” and crisp up with hot temperatures and Santa Ana winds.

Q: My ‘Double Delight’ blooms are typically a red and cream blend. This summer, the blooms are predominantly red rather than the red and cream blend. Why is this?

A: Blooms can change color in colder or hotter weather. ‘Double Delight’ will often be redder, with less cream, in hot weather. The unusual multicolored ‘Distant Drums’ has less pink and more apricot shades when it is hot and sunny.

Q: There is something seriously wrong with my blooms. Why do they look burnt and misshapen?

A: Chilli thrips, a pest, are most active in the hot summer and fall months in San Diego. The unmistakable signature of chilli thrips are blooms that look deformed, scorched, singed and burnt. Keep watching new rose growth daily and cut out and bag up all suspect blooms. Do not put your cuttings in the green waste.

Q: My rose has always had white blooms, but this year I am noticing that the blooms on one of the canes are dark red!  What happened?

A: The cane with the dark red blooms is in all probability a sucker, which is a cane growing from the rootstock, not from the rose’s bud union. Dig down, locate the origin of the sucker and forcibly pull it out or it will take over the bush.

Q: I checked, and the growth is coming from the bud union. Why have some of the blooms on my rosebush taken on a different color and form?

A: “Sports” are naturally occurring genetic mutations that can result in changes to the plant, including that of producing a bloom that is a different color or form. Tie a ribbon on the cane. If it keeps producing the new bloom variation, it may be a sport. A new rose variety can be propagated from the sport and can be introduced commercially as a new variety. For instance, ‘Secret,’ which is a pink blend rose, has a white sport that was commercially propagated and is named ‘Secret’s Out.’

Q: Why are there leaflike structures emerging from the center of my rose bloom?

A: Phyllody, or vegetative center, is one of the fun, weird blooms you will see in your rose garden, but there is no reason to be concerned. The cause is probably a temporary environmental condition such as hot weather, water stress or insect damage by pests. Your bush will resume producing normal flowers.

Leaf questions: insect and mite damage

Q: I am not seeing any pests on my roses, but on some of my roses the new rose foliage is misshapen and distorted and there are bronze streaks on the underside of the newer leaves. The blooms on the same bush look burnt and singed.

A: Chilli thrips are almost impossible to see with the naked eye, so we have to rely on the appearance of the pests’ rasping damage to the blooms and the new foliage to diagnose that chilli thrips are the culprits. This is a very hard pest to control and is most prevalent in the summer. Patrol your garden daily as the weather warms and cut out and bag all affected growth immediately. Some rosarians spray preventively in hot weather with pesticides that contain the active ingredient Spinosad. If you decide to spray, you must follow label directions to avoid harming bees.

Q: Why do my rose leaves look stippled, dusty and dry with fine webbing on the underside of the foliage?

A: Spider mites are hard to see, but your description indicates their presence. A spider mite infestation can also cause defoliation. This pest’s reproductive pace speeds up with the heat. When you catch the problem early, spider mites can be controlled with forceful jets of water directed to the underside of leaves three to four times a week. In prime spider mite season, remove the lower leaves on the rose bush that are very close to the soil. Picking up all leaf litter helps to disrupt their life cycle.

Q: Why am I seeing black grime on my roses’ leaves?

A: Black sooty mold is growth that forms as a result of the copious amounts of honeydew that is secreted by sucking insects like aphids, thrips, scale and whitefly. Control ant populations, as ants protect sucking pests from insect predators.

Q: Why are my roses’ leaves looking lacey?

A: Rose slugs look like small green caterpillars and feed on the underside of the leaf, leaving the leaves skeletonized. Squish them with your fingers or remove the leaves. Bacillus thuringiensis (Bt) will not eradicate rose slugs, because they are sawfly larvae and not caterpillars.

Q:  Why are my rose leaves rolled and tented together with silk?

A: Budworms and other caterpillars chew holes. Leaf rollers roll leaves and some caterpillars tie leaves with silk. Hand-pick them and clip rolled and tied leaves. Bacillus thuringiensis (Bt) is a spray that does not harm our beneficial insects, spiders or birds, but for it to be effective, the caterpillars will need to eat the plant growth you sprayed.

Q: Why are my rose buds chomped in half? Why are some new stems stripped entirely of all their leaves?

A: Grasshoppers and katydids chew leaves and blooms and can cause a lot of damage very quickly. They feed both at night and during the day. You can catch them, but you must be swift. One nurseryman told me he uses a short-handled badminton racquet to stun them before snipping them with his pruners. Practice makes perfect.

Abiotic leaf and cane questions

Q: Why are there tan and brown edges on my rose leaves?

A: Scorched leaves can occur in very hot weather when the rose plant controls water loss during transpiration by permanently closing stomata, or pores.

Q: Why do my leaves look burnt?

A: Fertilizing or spraying your plants with pesticides or fungicides in temperatures over 85 degrees can cause leaf burns. Wait for cooler weather to fertilize. And do not spray your roses with insecticides, fungicides, oil-based products or foliar fertilizers in hot weather.

Q: Why do the leaves on my container-grown roses look limp and wilted by the end of the day?

A: Container-grown roses need to be watered daily during the very hot months. One of the advantages of container plants is that many are movable and can be relocated to a cooler and more sheltered location in very hot weather.

Q: I am watering my roses, but the soil looks dry, and the roses don’t look hydrated.

A: When we water our plants deeply throughout the year, they develop deep root systems, which helps the plants reduce heat stress. Water in the morning to avoid loss of water through evaporation. Ensure that applied irrigation is penetrating the soil to the depth of the roots. Add an extra irrigation day during heat waves. Check to ensure that your irrigation is delivering water to all the plants and that emitters are not blocked. Apply a 3-inch layer of mulch to help retain moisture and keep the roots cool. In the early morning on very hot days, cool off your roses and wash dust off their leaves with an overhead shower.

Q: Why do my roses’ canes look sunburnt?

A: During hot spells, just snip off the bloom and leave all the foliage when deadheading. The plant needs as much foliage as possible to shade the bush and prevent sunburn damage on the canes. Do not remove old foliage and allow leaves to drop naturally.

Roses have their fair share of challenges in the summer. We can help by being observant to problems and remedying pest and water issues right away.

Perwich is a member of the San Diego Rose Society, a Consulting Rosarian and a Master Gardener with UC Cooperative Extension. For more advice on rose care, visit her website at rose-harmony.com.