A specialist pest or pathogen finds and builds on a continuous single-family host patch more readily than one broken by non-host families.
A good hunch · suboptimal if ignored → advise
How it works
Resource concentration - a specialist locates and holds its host more efficiently at higher host density and continuity, so an unbroken run of one family across adjacent beds is an easier target than the same family separated by a non-host (associational resistance).
What to do about it
Where one family fills adjacent beds in a single season, breaking the run with a non-host family between them lengthens the distance the specialist must travel to the next host. Disclosed, never docked: a continuous single-family block can be the right call anyway - a wind-pollinated crop like corn sets better massed - so the app names the trade-off and leaves the choice to the gardener.
How much it matters: No garden-yield figure is stated or invented. The resource-concentration effect is real for SPECIALIST herbivores and inconsistent for generalists, which is why it only advises rather than warns.
The evidence
Evidence: confirmed against 2 sources in the research-based literature.
the 2 sources
Root 1973, 'Organization of a plant-arthropod association in simple and diverse habitats: the fauna of collards (Brassica oleracea)', Ecological Monographs 43:95-124 (abstract read by the maintainer 2026-08-21): proposes 'the resource concentration hypothesis, which states that herbivores are more likely to find and remain on hosts that are growing in dense or nearly pure stands; that the most specialized species frequently attain higher relative densities in simple environments.' This is another rule here's claim and mechanism verbatim.
Elmstrom, Andow & Barclay 1988, 'Flea beetle movement in a broccoli monoculture and diculture', Environmental Entomology 17(2):299-305 (read by the maintainer 2026-08-21): the empirical test on a brassica specialist (the flea beetle Phyllotreta cruciferae) - immigration ~1.3x faster into monocultures than into dicultures, emigration ~2x faster from dicultures - reported as 'strong, direct support for the hypothesis that host plants are harder to find and easier to lose in vegetationally diverse habitats than in monocultures.'
Where this rule stops
THREE FAMILIES ONLY (nightshades, cucurbits, brassicas), scoped by applies_to.family - the same families the rotation another rule here/011/012 already cover, because those are where this corpus records specialist pest and pathogen pressure. another rule here is the SPATIAL, same-season sibling of that temporal rotation: another rule here/011/012 keep a family off ground it recently held; another rule here notes when one family runs unbroken across ADJACENT beds this season. It never docks a score (that would be the companion chart's diversity aesthetic smuggled in as arithmetic - the exact thing the bed-tools design refused); it surfaces as a composer disclosure beside another rule here and the rotation foreclosure.
Plants this fires on
- Arugula
- Butternut
- Cabbage
- Cucumber
- Eggplant
- Melon
- Mustard Greens
- Pepper
- Potato
- Radish
- Rutabaga
- Summer Squash
- Tomatillo
- Tomato
- Turnip
- Watermelon
- Winter Squash
Change history
Every change to this rule is one commit. This is what the project's version history records — the date and the reason — not a summary of it.
- verified: maintainer read Root 1973 + Elmstrom 1988 (invariant 4)
- the same-season adjacent-family pest-patch rule (approved 2026-08-13)
Cite this page
Milpa Gardens. "A specialist pest or pathogen finds and builds on a continuous single-family host patch more readily than one broken by non-host families." Evidence grade: A good hunch. https://milpa.garden/rules/specialist-pest-pathogen-finds-builds-continuous-family/
A garden-planning corpus: every claim states its evidence grade and links its sources on the page. Cite it with the grade, and add the date you read it.