Biological Control in Roses has been attempted for many years in Europe and North America. Results have ranged from fair to poor, despite active research on the part of growers and researchers. Recent research has shown the devastating effect of burning sulphur on parasitoids. This research confirms the Biological Control industries’ strong belief that the burning of sulphur is not complementary to the use of Biological Controls, especially in the case of Encarsia or other parasitoids.
Fungus gnats are an economical pest. The larvae effectively prune the fine, new root hairs, reducing the growth rate of the plant and its’ vigor. For roses grown in loose soil such as coco fiber, Stratiolaelaps scimitus, formerly known as Hypoaspis miles or, if allowed, Gaeolaelaps gillespiei, (now collectively referred to as Ss), should be applied to each pot at the time of planting. The rate should be 10 per pot, or 250 per square meter, whichever is less.
In an established crop, Dalotia coriaria should be added for control at a rate of 0.1 per square meter, just once. These mites, outdoors, will also control the rose midge in its soil-dwelling pupal stage.
The use of Monitoring/Trapping/Banking plants is essential in Rose production. Bush beans are extremely valuable. Thrips, spider mite and whitefly find the beans extremely attractive and, in many situations, actually pull the pests off the Roses. Both Encarsia and Delphastus find the beans to their liking, so, in addition to trapping and monitoring, the beans can become effective banking plants for these biological controls.
European cut Rose houses tend to be one or two varieties only. In North America, most houses, if not all of them, grow as many varieties as they can. Experience as shown us that some varieties are more susceptible to various pests than others. A log book should be kept to note when and where the various pests occur.
There is some indication that fungicides are having a negative impact on some Biological Controls, especially the parasitoids. Always attempt to complete your fungicide treatments before the application of the Beneficials. Growers should attempt to correlate pest increases with fungicide treatments about 1 month prior. This will help us determine if, and if so, which fungicides are having a negative impact.
Employees should be trained to spot spider mites and use a flagging system to identify their location. The section affected with mites should become the last section visited during the day.
In some facilities, spider mites tend to be localized. If the house has a history of spider mites, spread some Ss around every post, electrical and plumbing intersection. The Ss moves down into the ground and helps control the diapausing mites that are hiding there.
Bush beans should also be placed in these strategic entry points. The bush bean shows spider mite damage within a few hours, giving you an early warning system, and, in many cases, delaying the spread of the mites onto the crop. Overwhelmed bean plants should be carefully removed, and replaced. This technique is effectively “mopping up” the mites. Slowly developing infestations can also be managed by putting predatory mites on them, turning them into “banker” plants for the predators.
The primary spider mite control in Roses is Stethorus. This small black beetle loves Roses and cycles freely. It finds spider mites by smell and reacts quickly to new infestations. Stethorus should be released, throughout the sunny months, at a rate of 0.1 per square meter, monthly. Anystis baccarum should also be introduced to the crop at a rate of 0.25 mites per square meter in a clean house, or 0.5 per meter in a house with existing pest populations. Neoseiulus fallacis should be used throughout the greenhouse, preventatively, at a rate of 2 mites per square meter, just once, for the life of the plant. It should be applied as soon as the leaves open. The fallacis will control all known species of spider mite and will not interfere with the Phytoseiulus persimilis which should be directly applied to the hot spots. The typical release rate is 1 to 100 (predator to pest), for control within 2 weeks. Fallacis will permanently establish in Roses, over-Wintering with the spider mites and re-establishing themselves in subsequent years.
When a hot spot is discovered, push a Bean seed into the affected pot or pots, or, bring in a pre-grown Bean plant. The Spider Mites will move onto the Beans, if they are 2 Spotted, and take some of the pressure off the Roses. Pp should them be added to the Beans to create a Banking system. If the Banking system is active, leaves can be harvested from it and used elsewhere in the Greenhouse, in other hot spots.
Whitefly is an insidious pest. It only takes a few females, laying 300 eggs, to create a significant outbreak. The elimination of burning Sulphur has helped with Whitefly control, but, Roses still remain one of the toughest crops in which to manage Whitefly. This is due to the density of the foliage and possibly negative interactions with fungicides. Based on our observations, we suspect that fungicide applications are significantly impairing Encarsia performance.
In 2015 a BC Rose grower discovered that the beans that were placed as spider mite tools became infested with whitefly. Close monitoring showed that the beetle Delphastus and the wasp Encarsia both cycled freely on the beans, effectively becoming banker plants. The affinity of the whitefly to the beans is greater than to the roses, so, over time, the beans effectively pulled the whitefly from the roses to the beans.
This breakthrough is very important and effectively manages one of the toughest pests in Roses.
Release rates of Encarsia for Roses is 2 to 4 wasps per square meter, weekly. Delphastus rate is 0.1 per square meter monthly. Bean plants should be rotated no sooner than monthly and no longer than 2 months. Plant weekly batches of beans.
Aphids can cause considerable damage in roses. During aphid season, weekly releases of Aphidoletes aphidimyza should be made at a rate of 3000 per hectare (0.3 per square meter). Aphidoletes control and eliminate all species of aphids. They are excellent flyers and can find even just one aphid rapidly. If there is a high aphid population, care must be taken to release the preventative Aphidoletes in a “neutral” location, away from known aphid hot spots. This will force the Aphidoletes to disperse. The hot spots should be directly treated with additional Aphidoletes.
An eggplant will help considerably with aphid control. Eggplants will attract many of the incoming Aphids, seen as winged Aphids.
The problem of thrips in roses has drastically been reduced since debudding has become popular. Thrips still can come in a big way, and can cause considerable damage, but they won’t persist in the crop if all of the flower buds are removed from the house and Ss is present in the root zone, interrupting thrip pupation.
Neoseiulus cucumeris works well on roses, feeding on the first and second instar larvae. One application of cucumeris per month will maintain a constant level in the crop. Release rates are dependant on the level of contamination, ranging from 100 to 1000 per square meter. Slow release bags can also be used, but care must be taken to ensure that the bags are removed after 6 weeks to prevent the bran mite from causing damage in the buds. Using Anystis baccarum with N. cucumeris is shown to increase the predation of thrips. Unlike cucumeris, the anystis only needs a single application in many situations.
Strategically placed, flowering “Hero” Marigolds have been very effective Trapping plants for Thrips. During periods of significant Thrips, Marigolds should be placed throughout the house. Keep the Marigolds “topped up” with Ss in the soil and Nc on the leaves. If the plant becomes overwhelmed with Thrips, carefully place the plant in a plastic bag and remove it from the house.
Yellow or Blue sticky traps should have a cotton ball placed on them to absorb Vanilla or Almond Extract or Peppermint. These aromatic compounds can be very attractive to Thrips, and can increase trapping by a factor of 10. Trapping for thrips should always be low in the crop, even under the bench, for optimum thrips management.
Few crops are as difficult to manage pests in as Roses. The protected environment tends to hold out many natural enemies, such as Orius, as do the frequent fungicide treatments.
Most people don’t appreciated how much leaf surface area is present in this crop, so, as a general rule, release rates are frequently too low. Because of this, Roses must be managed with a strong preventative program. Stethorus and Fallacis for mites, Encarsia and Delphastus for Whitefly, and Aphidoletes for Aphids, all of these biological controls must be “fresh” product in order to ensure effective searching.
The use of Monitoring/Trapping/Banking plants will have a significant payback and will reduce the cost of monitoring.
Cucumeris in the crop against Thrips has an added value, as they are effective Spider Mite preventers, and also feed on Whitefly eggs if Thrips are not present.
All of the above mentioned Biological Controls are compatible with each other. Care must be taken if you wish to substitute any of them with alternate products.
Please also note that all of these strategies are based on our “fresh” non-refrigerated products. These release rates and application strategies will not work if you choose to use anybody else’s products. Please use their guide-lines for their products.