Add 4 independent seed brands: Latham + Stine + 1st Choice + Burrus (+623 varieties) (#17)

Co-authored-by: claude <claude@jpaul.io>
Co-committed-by: claude <claude@jpaul.io>

corpus/latham/latham-lh-5389-ss-rib.md

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+# LH 5389 SS RIB-NON RETURN
+
+- **Vendor:** Latham Hi-Tech Seeds (independent family-owned, Alexander, IA)
+- **Brand:** Latham Hi-Tech Seeds
+- **Crop:** Corn
+- **Relative maturity:** 103 days
+- **Trait(s):** Smart Stax
+- **Source:** https://www.lathamseeds.com/products/lh-5389-ss-rib/
+- **Rating scale:** numeric ratings ~1-9 where LOWER = BETTER (1 = best / most tolerant / most resistant); confirmed by cross-referencing Product Overview prose vs values (top-rated stalks/roots cluster 1.0-1.5, weak traits 3.0-3.5, none approach 9). Categorical values pass through verbatim (SCN source 'PI 88788', Phytophthora 'Rps 1k', Anthracnose 'ASR', 'Medium Tall', 'Flex'). NA/blank = not rated.
+- **Service area:** Latham dealer network — Upper Midwest (IA/MN/WI/IL/ND/SD/NE)
+
+---
+
+_Key attributes of LH 5389 are its excellent early vigor and strong Gosss Wilt and green snap scores. Flexibility across our 103-day maturity areas will create broad acceptance of this hybrid. You will like its high yield capabilty matched with a great disease package, which protects plant integrity all the way to harvest._
+
+---
+
+## Agronomic Characteristics
+
+- **Emergence:** 1.5
+- **Flowering for Maturity:** Equal
+- **Early Vigor:** 1.5
+- **Stalk Strength:** 2.0
+- **Root Strength:** 2.0
+- **Stay Green:** 2.2
+- **Drydown:** 1.8
+- **Test Weight:** 2.5
+- **Drought Tolerance:** 2.0
+- **Herbicide Sensitivity:** None Known
+- **Suggested Population:** 28-36
+- **Corn-on-Corn:** 2.0
+- **Ear Height:** Medium
+- **Ear Type:** Semi-Flex
+- **Number of Kernel Rows:** 16-18
+- **Cob Color:** Red
+- **Husk Cover:** Medium
+- **Shank Length:** Medium
+- **Leaf Angle:** Semi-Upright
+
+## Disease Ratings
+
+- **Goss’s Wilt:** 1.5
+- **Northern Leaf Blight:** 2.5
+- **Gray Leaf Spot:** 2.5