**6. Diseases and pest management**

Oilseed rape plants can suffer from a comprehensive list of enemies, starting with the viruses and finishing with mammalians. Their main fungal diseases are canker, light leaf spot, *alternaria*, and *sclerotinia* stem rot. The canker symptoms are leaf spotting, premature ripening and stem weakening in the autumn-winter period. The treatment of fungicides conazole or triazole is applied in late autumn and spring to fight this disease. The light leaf spot disease is caused by the fungus *Pyrenopeziza brassicae*. This disease can be recognised by speckles of white spore pustules on leaves, stems and pods, which become visible only after a period of dry weather. *Alternaria* fungi species causes leaf spots. It can penetrate the pods and infect the seed. *Sclerotinia* is dangerous when lower main stems are infected. Infection can stop the food and water supply to the canopy and cause the death of the plant. Broad-spectrum fungicides are used to control *alternaria* and *sclerotinia* development [1, 39, 40].

Also, oilseed rape can be attacked by a wide variety of insects. The most common insect pests that attack oilseed rape are the cabbage stem flea beetle (CSFB), *brassica* pod midge, rape stem weevil, cabbage seed weevil, cabbage stem weevil, and pollen beetle. CSFB is currently the main oilseed rape pest enemy. Adults of CSFB graze on young oilseed rape plants and can cause plant death. CSFB larvae also mine within the petioles and stems of plants. Lower chances of CSFB spread are considered in areas where oilseed rape has not been grown recently or nearby [3, 40].

Despite continuously developing CSFB management relying on a variable and complex set of alternative solutions, it has recently become more challenging to control. First, due to a reduction in effective chemical control options: resistance to pyrethroid sprays and the withdrawal of neonicotinoid seed treatments. Foliar application of pyrethroid insecticides was the most approachable chemical control of CSFB in oilseed rape. However, the resistance to pyrethroid insecticides is now widespread, and lessens the control's potential. Thus, when CSFB resistance to pyrethroid insecticides has developed, measures must be taken. Subsequent pyrethroid applications are recommended to avoid. This is to stop the selection for resistance and harming natural enemies [3, 41].

Otherwise, it is essential to follow the spray thresholds and cure a full field. The decrease in effective chemical options in oilseed rape has spurred the rise of CSFB. Reducing oilseed rape areas in certain regions is often associated with a higher prevalence of CSFB. Thus, crop protection requires innovation in this pest management. There is a need to find novel approaches to control CSFB, e.g., breeding varieties with greater resilience to CSFB, using biopesticides or others. Presently there are no varieties available to control any pest of oilseed rape. Little attention is paid to biopesticides to control CSFB have received. Biopesticides serve as a pest control option. They cause a minimal environmental impact, are specific to the target pest and can be a tool for resistance management [10, 40].

Oilseed rape is particularly vulnerable to pest damage at the early stages of growth. And it is far more tolerant to attack after the cotyledons have unfolded. The need for treatment can be determined by the number of shot-holing symptoms, leaf area eaten by beetles (**Figure 3**) or larvae and the plant's growth rate. Along with the adult beetle harm, the autumn, winter and spring CSFB larval assessment in leaf petioles and stem is present. It needs to be highlighted that the larval damage may be more economically harmful. Autumn larvae are more damaging, as their consumption of plant material last longer, and winter and spring larval invasion is likely to be less significant. If the risk is high –treatment at the first sign of attack is recommended to

**Figure 3.** *CSFB holing symptoms in oilseed rape.*

#### *Oilseed Rape: Biology, Use, Current Cultivation Issues and Agronomic Management DOI: http://dx.doi.org/10.5772/intechopen.109180*

be considered at the initial stages of growth. For the latter growth stages, such fields should be set up with traps, and the number of pests should be monitored not to exceed [1, 4, 6].

Effective chemistry is considered the best CSFB management option, however, no individual chemical or non-chemical approach is absolutely warranted. Thus, a combination of techniques is recommended for CSFB population suppression. Several alternative methods need to be mentioned. It is important not to damage natural enemy populations, e.g., ground beetles and parasitic wasps, by pesticide applications (especially broad-spectrum pyrethroids) and intensive cultivation. Great benefits were obtained in trials with trap crops. This approach uses trap crops to attract CSFB and simultaneously divert it away from oilseed rape. Afterwards, CSFB eggs or larvae die when the trap crop is destroyed. The disadvantages of this approach are that the use of relatively large areas of trap crops (at least 2 ha) is recommended and that the benefits can be variable. However, the trial approaches showed up to 88% reduced adult CSFB infestation and 76% reduced oilseed rape damage. It is recommended for a trap crop to be at an early growth stage at the end of August. This could make it more attractive to CSFB [40–42].

As an alternative solution, the selection of cultivars is recommended. The susceptibility or attractiveness of different varieties to CSFB has not been evidenced. Nevertheless, it is recommended to choose hardy varieties in the context of CSFB control. Such varieties can reach the four-leaf stage faster. This property makes the plant more tolerant to CSFB adult and larvae feeding damage [3, 4].

The maintenance of optimal soil humidity during crop germination is essential. Aiming to provide sufficient moisture levels, sowing dates should be adjusted regarding the soil humidity level and weather conditions and forecast. In addition to maintaining soil humidity and enriching the soil with organic matter, the cereal stubble and straw also have several benefits of their presence in the field for CSFB management. It is suggested that stubble and straw make it difficult for CSFB to locate the germinating oilseed rape and are useful as a support for spider web [1, 5].

The date of sowing is also shown to play a vital role in the CSFB management. Avoiding the alignment between beetle migration peak and the most susceptible crop growth stages is recommended. The sowing period of the highest risk from adult CSFB lasts from the end of August to early September. The early sowing ensures successful oilseed rape germination and establishment before the CSFB migration. The late sowing reduces an adult CSFB beetle feeding damage by moving the germination after the migration peak and reducing the larval invasion by slowed egg laying and development under cooler conditions. Studies have shown that a 10-fold reduction in larval invasion is obtained by a three-week postponement of sowing.

The optimisation of seedling density can also be used to reduce the risk of CSFB damage. To achieve final optimal plant density under the threat of CSFB invasion, the seed rate needs to be increased. And on the other hand, by decreasing the seed rate, plants may grow larger and more tolerant of larval feeding in the spring [6, 34].

Companion crop species are known to prevent or lessen crop damage by attracting the pest, improving soil, masking the crop from pests, or offering shelter for natural enemies. For example, mustards act as sacrificial plants that are eaten first. The research on CSFB management has detected significantly lower damage in two-leaf and five-leaf stage oilseed rape cultivated with a list of companion crop species. Buckwheat, legumes and *Brassicaceae* family members are known to play a preventing role in CSFB management. The companion crop should be sown about a week before oilseed rape and can be removed by frost or by the herbicide. It should also not outcompete oilseed rape [3, 7, 41].

As CSFB larvae generally settle in leaf petioles, trials have shown that managed defoliation reduces larval invasion by up to 55%. It has also been found that sheep grazing and topping/flailing are effective in reducing larval populations. The most beneficial is late defoliation before stem extension (November and December). Later defoliation could be dangerous due to a lack of time for plants to recover. It is also suggested that CSFB damage could also be reduced by the addition of organic amendments during the establishment period. The use of organic amendments may be helpful to for CSFB invasion management by improving plant growth, masking the crop, and repelling the pest. Moreover, crop tolerance to larval damage can also be enhanced by proper nutrition and plant growth regulation. It should be noted that the management tools proposed to control the CSFB spread are also useful in eliminating many other issues in oilseed rape cultivation [12, 40].
