PP 1/331 (1) PRINCIPLES OF EFFICACY EXTRAPOLATIONS FOR MAJOR USES

weeds grown outdoors are usually hardened off and

therefore less sensitive to herbicides.

The effectiveness of soil-acting herbicides against

weed species in the field cannot be extrapolated to use in

potted plants. The effectiveness of herbicides (whether

contact or soil-acting) cannot be extrapolated from use

either outdoors or in potted plants to use in artificial

substrate. This is due to the likelihood of different im-

pacts on effectiveness arising from different growing

media.

Appendix

(Figure

) presents a scheme to

be followed for herbicides major use effectiveness

extrapolations.

CROP SAFETY

3.1

General principles for extrapolation of

crop safety

Crop safety can vary considerably between crop spe-

cies, and cultivars. The following points should be

considered:

•

Are there any crops where the product has an authori-

sation on a crop taxonomically related to the new

crop?

•

Is the architecture of the crops concerned similar?

•

Are the agronomic growing conditions similar?

•

Are there adequate crop safety data for the crop(s)

from which extrapolation is required and across a

range of cultivars?

•

Are there any issues with phytotoxicity on other

crops?

•

Is the use (e.g. dose, water volume, timing) the same

or sufficiently similar for the crops involved in the

extrapolation?

•

What is the mode of action of the active substance?

•

What evidence of phytotoxicity is available from stan-

dard pre- and post-emergence pot tests and glasshouse

varietal screens? Conditions in a greenhouse can af-

fect the structure of plant surfaces, as well as biology,

thereby changing the crop safety of a product. A case

for extrapolation from the greenhouse to the field may

be valid but caution is required. In some cases the pro-

tected crops may be more sensitive (perhaps because

of a thinner layer of surface wax). In other cases the

damage on outdoor crops may be influenced by fac-

tors not found under protection (e.g. sudden tempera-

ture changes, frost, abrasion by soil particles, wind,

drought or water-logging).

Extrapolations may not be possible, for example,

where the product has shown crop damage on some

crops, where the crops concerned are significantly dif-

ferent, or where the crop is known to be particularly

sensitive. In these cases, a full crop safety package is

required.

3.2

Specific crop safety extrapolations for

fungicides and insecticides or acaricides

As a general principle, insecticides, acaricides and fungi-

cides would be expected to have limited adverse effects

on the crop. The extent of extrapolation between crops is

largely depending on the use of the product, known sen-

sitivity of the crop or the growth stage, and the depth of

existing knowledge of the crop safety properties of the ac-

tive or the product.

Evidence may be available from pot tests and green-

house varietal screens from preliminary data for the

active substance. This provides a baseline of inherent

crop safety properties. Observations for phytotoxic ef-

fects should be made in the direct effectiveness trials

and usually no separate selectivity trials are needed.

However, if any adverse phytotoxic effects occur in

some effectiveness trials at the authorized dose, then

the effects of the double doses should be investigated

and specific crop safety trials should be conducted (see

PP 1/135

Phytotoxicity assessment

). Using this combi-

nation of greenhouse and field data, information can

be built up on a range of uses and perhaps formulation

types, allowing scope for extrapolation to other crops

in the absence of further crop safety data. Where the

active or the product is known to cause significant

symptoms or has existing label warnings, or the pro-

posed extrapolation involves crops of known sensitiv-

ity, further limited data may be needed to support the

extrapolation.

3.3

Specific crop safety extrapolations for

herbicides

For major uses, extrapolation between crops is not rec-

ommended, without crop safety data carried out in ac-

cordance with relevant specific EPPO PP1 Standards.

If a herbicide is demonstrated as only effective

against monocotyledonous weed species, it may be

possible to extrapolate crop safety between different

dicotyledonous crops. However, this will depend on

information available on the crop safety of the active

substance.

If there is no crop exposure, crop safety data may be

extrapolated between crops. This will depend on whether

the herbicide is systemic, its route of uptake and the

method of application. Shielded application, inter-row

application (depending on timing), and spot application

are examples of not exposing the crop to herbicides.

SEED TREATMENT

Extrapolation between seed treatments of different

crops is normally possible when seeding density and

thousand-grain weight are similar and if a pest causes