Gardeners have been experiencing more rose diseases and critters never before seen in the southwest Riverside County region. Many are caused by invasive pests hitching rides on planes and ships from faraway regions, often with disastrous results.
One recent example, in my opinion, is the cancellation of the Palm Desert Rose Show in November 2022 because major exhibitors said their roses had suffered severe damage from chilli thrips fostered by unseasonably high fall temperatures. To the best of my knowledge, it was the first such cancellation in my nearly 40 years of growing roses in the Pacific Southwest.
The chilli thrips are spreading rapidly in the southwest and are becoming a global threat to roses. It is even smaller than the western thrips we’re familiar with – so small that it cannot be seen with the naked eye. It works in similar ways, only more devastating and more difficult to control.
The chili thrip doesn’t seem to have any preferences except new growth of almost any plant and blossom. Its damage resembles the effects of pesticide overspray or rose virus: severely stunted and very narrow leaves, stems and buds.
This pest is prolific, especially during hot temperatures in July through October, and is particularly resistant to conventional control methods. Gardeners I’ve spoken with use products containing Spinosad, such as Conserve, to gain some control. Infestations have been sporadic with severe to mild being reported.
If you’re in this situation, the only practical road to control is to prune out the affected parts and consign them to the green waste bin. Then immediately apply a chemical insecticide spray and begin a spraying program as directions indicate or, every 7-10 days until control is reached, then at two weeks intervals. Always follow the directions on the container carefully.
Roses were still actively growing and blooming in many Temecula Valley gardens during the Thanksgiving holiday, as most areas haven’t had low temperatures near frost which, on average, occurs in mid-November. Normally, lower nighttime temperatures cool the soil and reset the roses’ biological clock to slow down and go into a kind of dormancy.
Roses need a four- to six-week dormant period during the winter months to allow them to undergo natural hormonal changes that prepare them for the next growing season, including forming buds at the base of the plant to produce new canes. At this point, aside from pruning away dead or diseased branches, I encourage you to not deadhead or prune until late January to early February.
Be sure to monitor your plants when daytime temperatures are warm: They still need to be kept hydrated. Also, do not fertilize until after your major pruning in January or February. I’ll provide thorough information on all that early next year. Speaking of fertilizer, the San Diego Rose Society is currently taking annual fertilizer orders for January delivery to have on hand when new spring growth is 2-3 inches long. For more information, visit https://www.sandiegorosesociety.com/fertilizer-sale.
There is still time to order that new rose you have been dreaming about. Garden stores may still be adding to their list of orders, or visit your favorite online nursery and make your order. There are many fine new roses that you simply must have. Many are more disease resistant than in the past.
Most nurseries or wholesalers no longer print catalogs, so for a list of current roses available from each you will have to go online. You can view the varieties that each will be stocking by going to their website.
A few new varieties I find of interest are: At Last (floribunda, good apricot color, fragrance, disease-resistant); Bordeaux (floribunda/wine red, large blooms, heat tolerant, disease resistant); Easy Spirit (floribunda/White, Hybrid T form, fragrance, hybridizer Tom Carruth, disease resistant, lasting form); Frida Kahlo (floribunda/Scarlet Red striped gold, small clusters, mild fragrance, disease resistant, compact, hybridizers Christian Bedard & Tom Carruth); Gaye Hammond S (Bright Yellow with touches of orange, slight fragrance, disease resistant, bloom making machine); Parade Day (Grandiflora/Fuchsia Pink Striped White, strong fragrance, hybridizer Christian Bedard, holds color); Flowerland (Shrubby, Pink, low (1.5 foot) growing habit, 60-65 petals, fragrant; it would be great for small spaces or en mass) and Golden Iceberg (mild spicy fragrance).
For more ideas, visit Temecula Valley Rose Society’s Rose Haven Heritage Garden at 30592 Jedediah Smith Road, in Temecula, as well as at http://TemeculaValleyRoseSociety.org/index.shtml.