Oils

• Neem oil is derived from neem tree leaves and is a highly effective, organic insecticide. The oil kills aphids on contact. Cornell University reports that various studies suggest neem-based products provide good control of turnip aphid, poor control of the green peach aphid and mostly good control of most other aphids. Apply neem to the undersides of leaves, new growth and other places that aphids colonize. Neem oil products are available at many garden centers.
  
  

Soaps

• Insecticidal soaps and horticultural oils kill aphids on contact. They are especially effective at controlling populations before an infestation has occurred. Spray them over areas where aphids frequent, particularly on the undersides of leaves. According to Cornell University, studies suggest soaps are mostly effective at controlling most aphids, but ineffective at controlling the green peach aphid. Combine 1 tbsp. dish detergent with 1 qt. of water and apply the solution with a spray bottle.
  
  

Other Organic Solutions

• Pyrethrum is an organic pesticide substance derived from the chrysanthemum. It is approved for indoor use on vegetable gardens, and many commercial pesticides contain this substance. Although it shows some control over aphid populations, it may not control aphids on spinach plants, and studies suggest it is not as effective as other organic applications. Some organic growers claim that pyrethrum is not good for organic gardening because it kills beneficial insects that otherwise control aphid populations.
  
  

Other Controls

• Monitor and prevent aphid populations from overwhelming crops. Encourage beneficial insects that consume aphids. Manipulating the environment encouraging their presence and providing their sources of food help boost predator populations. Inspect overwintering plants brought into the greenhouse, which are often infestation sources. Control weeds in the growing environment.