Propagation/Greenhouse ManagementUnit 1.3 | Part 1 – 111
Lecture 2: Managing Environmental Conditions
- Good cultural practices are a critical component in the management/prevention of pest/
disease challenges
a) Select pest- and disease-resistant varieties and avoid crops vulnerable to known
potential problems. Check with local growers and extension agents for issues common
in your area for the crops you grow.
b) Grow crops at appropriate seasonal junctures, where environmental conditions
naturally facilitate healthy, vigorous, pest- and disease-resistant growth
c) Manage environmental conditions to mitigate against the presence of pests/disease
and promote vigorous, uninterrupted growth. This includes the management of:
i. Temperature: Especially important in the prevention of damping off organisms,
which thrive when soils are constantly moist and temperatures are steadily in the
68ºF to 86ºF range. While this range is both ideal for damping off organisms and
for the growth of many common crops, damping off damage can be prevented by
using high quality soil media, making sure the soil goes through adequate wet to dry
swings, and sacrificing optimal temperatures when cooling will control damping off
fungi.
ii. Moisture: The quantity and frequency of moisture delivery is critical to healthy
seedling development. Constantly wet soil deprives roots of necessary oxygen, limits
the mobilization of organic nutrients in the soil mix, and can create conditions that
favor damping off and root rotting fungi. Excess irrigation can also lead to nutrient
leaching from the soil media, depriving plants of valuable resources and potentially
compromising local surface or groundwater quality (see Supplement 2, Conserving
Water and Protecting Water Quality).
iii. Air circulation: Circulation or oxygen exchange within the greenhouse, as previously
highlighted, helps regulate greenhouse temperatures, is critical in promoting strong
cells and healthy growth, and prevents pathogen buildup
iv. Fertility: In concert with other cultural practices, adequate but not excessive soil
fertility promotes healthy, uninterrupted growth. Excess fertility can lead to lush,
rangy growth and attract aphids and other insects that feed on nitrogen rich crops
(see Appendix 6, Sample Soil Mix Recipes, for examples of mixes with appropriate
fertility).
- Management also includes monitoring and early detection of pest/disease problems to
minimize crop loss and need for intervention
a) Monitor at regular frequency: Make close observations to look for early signs of disease
and pest presence; use yellow or blue sticky traps to sample for and or control flying
insects such as shore flies and fungus gnats
b) Use pest and disease identification tools such as the books and websites listed in
the Resources section of this unit (see also Unit 1.8, Managing Arthropod Pests and
Unit 1.9, Managing Plant Pathogens). These resources can help with understanding
life cycles, seasonal and environmental conditions that favor pests and pathogens,
cultural strategies that can prevent or minimize problems, and in some cases, suggest
organically approved inputs to use when intervention is necessary.
c) Establish clear tolerance thresholds to initiate control actions, when shifts in cultural
practices and environmental management does not provide adequate controls
d) Rogue (cull), or quarantine infected crops to prevent the spread of problems to nearby
crops susceptible to the same pests or diseases. Roguing requires sacrificing some
for the good of the whole. Quarantining allows treatment strategies to be applied
selectively and in isolation from other susceptible crops, thus reducing the likelihood of
more widespread outbreaks.