**4. Cultural control of cereal aphids**

Cultural practices can play a significant role in IPM strategies targeting cereal aphids. Cultural controls are generally the cheapest of all control measures because of their preventive measure and only require modifications to normal production practices. They do not possess some of the detrimental side effects of pesticides, such as killing of beneficial insects, no contamination of environment and development of resistance to pesticides [17]. Modified cultural practices can be important in minimizing cereal aphid infestations which include dates of planting, seed rates and fertilization to produce the healthiest crop possible.

In Kenya, studies on use of cultural control practices such as time of planting as alterna‐ tive strategies for control of aphids to reduce cereal aphid populations have been assessed. Cultural control of aphids and its effect on the incidence of cereal aphids was addressed through research, especially the assessment of time of planting and subsequent cereal aphid population levels. Three planting dates were evaluated, namely, early planting (April), medium planting (May) and late planting (June). The data (**Table 2**) indicates that for late planted wheat crops, Russian wheat aphid density levels were very high and the resultant grain yields very low [30]. Seasonal mean aphid population was 7.4 and 2.1 times higher on late as compared to that on early and timely sown crop, respectively (**Table 2**). This indi‐ cates that changing sowing date of wheat will affect cereal aphids infestation, thus planting date may be adjusted to minimize cereal aphid infestations. The study also showed that early planted wheat crops escape heavy cereal aphid infestations and give good yields. It has been recommended that wheat growers should sow their crops early to avoid damaging levels of Russian wheat aphid and other cereal aphids. In addition, it is important to note that sowing should be done early in the season so that the crop benefits from the early rains and it should be timed such that harvesting coincides with the dry spell. The potential of cereal aphid infes‐ tations can be reduced by sowing wheat crops early in the season [1] and also cereal aphid infestation increases on late plantings and reduces yield as compared to normal planting [3].


Continuous cropping of wheat was practiced by wheat growers in Mt Kenya region, eastern Aberdares ranges and West Mau areas of Kenya [31, 33]. This enabled cereal aphids to migrate from one field to another and survive from one season to the next. Similar observations have been reported in wheat growing areas in the highlands of Ethiopia [40]. It was also observed that the different crop planting dates and eco‐zones across the country as well as the presence of volunteer cereals and alternate host grasses provide a continuous source of alternative host plants and consequent spread source of cereal aphids to wheat crops planted the following season. The information being generated from field surveys has been used to advice farmers when to plant and which control options to adopt in order to escape the damaging species of

Key: \*Dn – *Diuraphis noxia*; Md – *Metopolophium dirhodum*; Sa – *Sitobion avenae*; Rp – *Rhopalosiphum padi*;

**Mt Kenya area** *+++ ++ ++ ++++ ++ +* **Mau Narok** *++ + + ++ ++ +* **Nakuru** *++++ ++ ++ +++ ++++ +* **Narok** *++++ ++ ++ +++ ++++ +* **Trans Nzoia** *+++ ++ ++ +++ + +* **Uasin Gishu** *+++ ++ +++ +++ +++ +*

*Incidence:* ++++, highly abundant; +++, moderately abundant; ++, abundant; +, low abundance.

**Table 1.** Incidence of Russian wheat aphid and other cereal aphids in wheat growing regions of Kenya.

**Dn\* Md Sa Rp Rm Sg**

**Region Incidence of cereal aphids species**

Rm – *Rhopalosiphum maidis*; Sg – *Schizaphis graminum*.

214 Wheat Improvement, Management and Utilization

Cereal aphids also have preferential performance on different hosts. Results observed in Kenya [49] revealed that aphid species differed in their time of colonization on wheat varieties. Aphid abundance differed among the species, wheat varieties and crop growth stages*. R. padi* appeared at two leaf stage, followed by *S. graminum* at the two tiller stage and *M. dirhodum* appeared at stem elongation stage. The aphids also differed in their points of colonization, thus the studies

Cultural practices can play a significant role in IPM strategies targeting cereal aphids. Cultural controls are generally the cheapest of all control measures because of their preventive measure and only require modifications to normal production practices. They do not possess some of the detrimental side effects of pesticides, such as killing of beneficial insects, no contamination of environment and development of resistance to pesticides [17]. Modified cultural practices can be important in minimizing cereal aphid infestations which include dates of planting,

confirmed crop growth stage and feeding preferences among cereal aphids in wheat.

seed rates and fertilization to produce the healthiest crop possible.

cereal aphids.

**4. Cultural control of cereal aphids**

**Table 2.** Effects of time of planting on Russian wheat aphid densities and wheat yields at Njoro, Kenya (2160 m.a.s.l.).

The effects of sowing dates of planting dates and insecticide sprays on aphid populations and barley yellow dwarf incidence in Kenya were also assessed [57]. The most common important cereal aphids observed included *M. dirhodum*, *R. maidis*, *R. padi*, *Sitobion avenae* and *S. graminum*. BYD incidence was significantly decreased in plots sown with seed that had been treated with imidacloprid and later sprayed with cypermethrin foliar insecticide. Yield losses due to BYD were also significantly different between the treatments and between the early planted and late planted crop.

Field trials have also been conducted in Njoro, Kenya [47, 48] on development of environ‐ ment‐friendly and cost‐effective cultural practices (utilizing seed rates and fertilization levels) for management of RWA in order to reduce/avoid use of chemicals in wheat production. It was observed that a combination of moderate seeding rate (100 kg/ha) and application of nitrogen (100 kg N/ha) was observed to be the best for the cultural management of Russian wheat aphids in wheat production. To minimize dependence on insecticides for cereal aphids' control, cultural practices like adjustment of planting dates and seed rates may be helpful.
